As some of you know I picked up an EO Tech 552 (military AA battery powered model) for a very good deal a few months back. One issue that keeps getting brought up is the the battery life (especially compared to the outstanding Aimpoint M2). Doing some spec checking on the EO Tech website, the sight is listed to run 500 hours with the Lithium batteries, just over 300 with standard Alkaline batteries, and a bit over 200 hours with rechargables (NiMH). The problem is they list the times at the 'On' setting of 12. Also note all times were based on Energizer brand batteries.

FYI Energizer Brand AA Battery Storage capabilities* (milliAmp/Hour & weight):
Lithium 2900mAh, 29g
Alkaline 2850mAh, 46g
Alkaline (E2) 3135mAh, 46g
NiMH (rechargable) 2100mAh, 54g
*Data from www.Energizer.com

That setting (12) is fine for indoor use, or in low light situtations, but you won't see the reticule during the day. I found durring Giles & Petes Carbine 2 I often had the sight set at 16 or 17 during the day ('On' +4 or +5). So I decided to run some tests with the sight running at realistic levels.

I had pleny of NiCad's but few NiMH battieries so I went out to buy some specifically for this test. I settled on Energizer brand NiMH. They came 4 batteries to the pack and it included a fast (1 hour) charger, all for $20.  When I got home I plugged it in and charged them up. After the batteries were charged up I installed them in my EO Tech and turned the unit on (8hrs) and pressed the 'Brighter' button 4 times (setting 16). I kept on repeating this procedure many times over the next 12 days. Some times I would go +4, other times +5, and I often carried the sight to work with me and slept next to it so I could check on it peridically and verify it didn't die. Here are my results

I was able to run the Eotech for twenty (20) eight (8) hour cycles. Almost half those cycles were at setting 16 (cycles 1 through 8, and cycle 20), the rest were at setting 17. This was done over a period of 12 days (so most days had 2 cycles). On the last day (yesterday) I started the sight (cycle #21) at setting 16 at 20:10, it was still running at 23:05, but dead by 02:30 today. The sight would not 'restart' after it died untill new batteries were installed. EO Tech lists as one of their 'advantages' that there is no muzzle side signature. They may be true on the NV setting, but when the sight is set to 16 you CAN see the reticule from the front (in a darkened room) to at least 10' [and I suspect much more but I ran out of space]. However to see it - the reticule had to be aiming right for your eye, if you were off axis just a bit you could not see the reticule.

I should note the EO Tech has a low battery indicator when the batteries reach 20% of capacity. To signal this the reticle blinks for a few seconds when the unit is turned on. The reticule started blinking on the 3rd cycle.  The low battery indicator might work great for Alkalines - but its useless for NiMH batteries (as they operate at a lower voltage).

What does this mean to the EO Tech user? IMHO it means the EO Tech can be a very reliable sight for the LEO user. By starting the unit at the start of a shift the sight will be on when its needed, and it will turn off automatically at the end of an 8 hour shift. If you're on duty longer just hit the 'bright' button for another 8 hours. The LEO should swap batteries
weekly. Even at double shifts the EO Tech will be able to handle 7 days of 16/hours a day with no problem, and there will be no worry of the sight losing power.

Now for some interesting numbers. NiMH are good for up to 1000 recharges and they have no memory problem (unlike their NiCad cousins). Based on weekly use, and a life of half what is possible, those 4 batteries should be all the power that is needed for over 19 years. However reality sets in as the chemicals in the battery just won't last that long; however you will get
several years worth of work from those 4 batteries.

I've started 2 more battery tests. I had pulled out the 2nd pair of batteries from the Charger last Thursday night. When I installed them into
the EO Tech and powered up the sight I was getting the lower battery warning.  According to Energizer I should't have lost more than 10-15% of the charge while the battery sat on the shelf. I plan on seeing how many days I can go starrting out this way.

I also took the spent pair of NiMH's and put them in my $20 solar recharger.  Normally this is used for Ni-Cads for the kids toys - but I thought I'd try it out with these newer batteies instead of buying another solar charger.  I put the pair in the charger this morning and set the charger on the dash of my Jeep. I plan on driving around for a few days to see if the charger will recharge the batteries  sufficiently. According to my chart the charger should be able to recharge the  batteries in 4-6 hours given full sunlight. On the dash they won't be getting optimal light as I can't insure a good angle & southern exposure. Should be interesting.

Note this testing applies to EoTech 552/512 series that are rev E or greater; earlier models could not run with Nickle-Metal-Hydride (NiMH)batteries.

Very good info!

Forest, that is an awesome review.

Thank you gentlemen - comming from you two that means alot to me.

Forest,

I like the way you operate.

w-w

Forest,

Bravo! Excellent testing and write-up!  

IMHO, the autoshutoff on the EOtech is invaluable.  An aimpoint may get more batter overall battery life, but lacks that feature.

If you accidentally leave both on after a day at the range or end of a shift, or even gets turned on in the bag, which one will light up next time you need it?  Not the aimpoint.

I have a little N battery EOtech, but I dont worry at all.  If I leave it on, it turns off.  If the batterys get old, it blinks and I stop at walmart.  All battery devices should be so designed.

TJ

THESE are the kinds of posts that truly make this sight worth the time.

Good job Forest.

[b]DITTO![/b]

Good job Forest. If in the future I ever give you a smart-ass comment in a thread, remind of this. Ok? Buddy!

Thank you all for the warm comments.

The solar charger is a $20 charger I got a number of years ago from Real Goods (www.RealGoods.com IIRC).  They no longer sell that model now (though they do sell a similar unit).

I tested my batteries a few minutes ago.  After a day in the sun (with the car mostly parked facing North on a sunny day).  I was ableo to get the sight to light up - but it was blinking on startup.  My goal is to charge it enough so it doesn't blink (then I'd know I'm in the 92%-100% charge range).  Tomorrow I'll park with the vehicle facing south and see how it goes.

Spooge - don't worry about any smart a$$ comments if I deserve it.  If I don't think I do then I'll just fire one back [;)].

I've run my Aimpoint for a month solid with my semi-routine "in the safe battery test" [:)] - but I still change out my batteries out every year even though they survive the test.

Forest try the Brunion soalr charger that runs about $40 which works for me ... in ever sunny California.

YES!  An excellent post!

Ive had my 551 for over a year now and have not changed batts.  I shoot on average 4 days a week for about and hour or more give or take each outing leaving the sight turned on from the first shot till I quit.  This is done in both night (some NV) and day lighting conditions so of course my settings vary depending.  I have been quite surprised since I assumed the batteries would have died long ago.

Of course now that I said this it'll probably be blinking at me tomorrow[:)]

I bought My CompM, non XD model, withen a week on the first ones comming into the county, several years ago now.  It's still on its first battery and I forget to turn the thing off pretty regularly.

My Bushnell Holosight II used up it's first set of batteries pretty fast.

This is the most "useful" post about the Eotech I've seen in a very long while. Outstanding job, Forest!

Useful data and facts instead of spouting off opinions on the same subject over and over again? Man what is becoming of this forum? [;)]

Good stuff Forest.  Thanks.

Wow that's pretty darn good!  Is it mostly on or do you normally keep it off (turning it on only when needed?).

One of the things I liked about my Reflex & TA50-2 was they were always 'on'.  This was a test to see how well the EO Tech would do in that role.  When you grab your rifle you don't want to have to remember to fiddle with the controls to turn it on & adjust it while your watching the threat.  The idea is you turn your sight on at the begining of your shift (LEO Patrol, guard duty, etc) and leave it on the whole time.  The test has determined how many days/cycles you can go before needed to swap batteries (it would be a bummer if power went down in the middle of a shift eh?).

So I've come up with above protocol to insure an EO Tech is never without power.  

I would be interested in seeing a similar test for the Aimpoint - say leave it on a good daylight setting and leave it there, check every 12 hours to see if its still on.  It would be interesting to see how often you'd have to change the battery and what that would cost over a couple years.

Forest, you just sold me on an EOTech!  

Thanks for the great and very useful info.

NEVER EVER EVER!!!!!!!!

Let your NIMH batteries stay dead!

If your going to store them, store them with a full charge. NIMH does not develop memory, but they need to be charged and never stored empty.

Problem is NiMH batteries won't hold a charge forever.  This is what Engergizer has to say about storage of NiMH (note they just recommend removing the load - nothing about storing charged or not).

That's dedication (20 cycles)

I actually find that setting 14 is brighter than I need even in the day.
[b]Odds are the lithium AA's would last long enough to try the patience of the most dedicated tester.[/b]


Aimpoint comparisons would not be very valid as the aimpoint dot nearly washes out for me at the highest setting.  

Oh and yeah there is no free lunch both sights will project the light forward if they are at high settings in the dark.  (but setting 14 is very bright on the EO in the dark so odds are you wouldn't have it there.) Same goes for the aimpoint the brightest setting is a little too bright for nightime use (unless you know you will be using a flashlight.)

Green,
Yeah 16 & 17 are a bit high for night use.  IIRC when I was using my 120 lumen bulb in the G2 I set the EO tech to 14 or 15 since we were often really close to the targets & walls.  Backsplash from the light would degrade the reticule so I would set it brighter.

[b]On storage of NiMH batteries[/b] I contacted Energizer with the question of do I need to store the battery charged, and how long can I warehouse NiMH batteries (assuming room temperture).  Here is their response  (and my orginal e-mail below that):

Pay particular attention to Paragraph 10 (they can be stored indefinately charged or not).

I read on another thread that someone has had their Aimpoint on for about 7 months now.  Mine's been on since the 18th. I, too, want to see how long the battery lasts.  Doesn't sound like the Aimpoint needs a battery shutoff [;)] and I like the fact that it's on when I pick up the rifle.  

I can recommend a smarter charger for more regular use.  I abuse...I mean use... NiMH AA and AAA all the time.  I hardly ever completely discharge them.  Whenever I feel they are less than tip-top, I top off a new set and replace.  The discharged ones go into the charger than back into storage.  It may me a little more work than is necissary, but it keeps all the cells in storage in a known state, and I cycle through the cells at least once a month.

Standard rule of thumb for NiMH self-discharge in storage is 1% of capacity per day.  It isn't a linear curve.  It's pretty quick to reach 75% and then slows before it hits 25%, but usually after a month of storage they are below 75%.

I have no idea of the specs on the charger you have, but a smart charger like the Maha 401s will keep the batteries in a float state after a full charge, checking them periodically and applying a slight charge if needed to stay at 100%.  It also rarely makes the cells hot to the touch.

Today's report.  Well today in MD I kept the Jeep pointed south - but we had an overcast sky.  So the batteries still are not full (I tried them in the EO Tech).

I'm sure they will eventually be charged, but I was hoping for 2 days or less.

Another option I have is to plug my smart charger (the one that came with the batteries) into the car directly.  Input in the unit is 12VDC.  I should be able to go to Radio Shack and get the plugs I need.  Then the charger would work plugged into the wall or the cigarette lighter.

great info forest, thanks!
my aimpoints sometimes turn on accidently when the switch rotates when putting the rifle back in gun cases, and i've drained a battery once.  i'm with u guys - the auto-shut off feature of the eotech rocks!
cheers,
MM

[b]Update[/b]
Well yesterday it was cloudy do I didn't even check it.  Today I went out to the car around lunch time to check the batteries.  Car had been facing South and in full sunlight for 2.5 hours.  Batteries still hadn't reached the 92% mark (reticule was blinking).

I put the batteries in the charger and plan on resting them tonight.  If they are not charged satisfactory tonight I'm going to look at a new charger (the one that was mentioned earlier).

I also am 'topping off' the other pair using the Energizer charger running from the 'power outlet' in my Jeep.  I pulled the cord from my scanner and it works great.

[b]Update II[/b]
Ok Friday night (after a full day of sun facing south) my batteries still were not fully charged.  I got 3 full 8 hour cyles (at 17) then slightly less than 2 hours on the 4th cycle (again at 17).

I'm going to test a new solar charger and get back with the results.

Good news is the Energizer charger works great when plugged into a car (I used the 12v power cord from my scanner, didn't even need to go to Radio Shack).