Or is it fine to leave the battery tender on full time for a 12v deep cycle that sits unused on my shelf for 10 months of the year?


batteryminder plus model 12117

this one

Important specs

Amps1.33
Trickle Charge Amps5mA–1A determined by battery demand


Batteries I will use it on.

1- sealed rechargable out of a UPS-- 12v, 9.0 amp hour

2- everstart marine-- 12v 845 max cranking amp, 114 amp hour @ 1 amp

what is the amp hr capacity of the battery and how many amps is the charger delivering?

If it's a quality tender (not a trickle charger) that monitors battery voltage and cycles itself in and out of float mode, yes, it will work fine on a deep-cycle battery.



I use 'Battery Tender' model.



 

You can. Honestly, even the quality tenders are likely somewhat harmful for a battery over a
very long duration.

I'm a bit of a battery nut due to some of the past work I did, the issue is that most batteries like
high-current charging, which makes the electrodes inside the battery spongy. If you do a lot of trickle
charging, it's lower current and more like electroplating, e.g. it's not spongy. It can also lead to internal
shorts because high currents break things up and low currents don't. This translates to bulk mode
(high current) v. float mode (low current) charging. The best thing for batteries in general is to not
have too much of anything, so ideally you'd actually use the battery occasionally to a reasonable
depth of discharge, and then do a conventional charge (bulk + float) and then disconnect it.

I have a calendar item to exercise and charge my batteries once every 4-6 weeks or so, but as
I said, I'm a battery nerd. My cycle is to run a high-current device for a while until I see about a 25%
depth of discharge, and then do a full charge cycle and then disconnect and store the battery.

It's also important to set your charging current correctly, a little 7Ah gel cell needs a completely
different current (both bulk and trickle) than a 100+ Ah golf cart battery does.

Will get some numbers and post them for further wisdom.

put that trickle charger on a mechanical timer....run it for 15 minutes a day.



Problem solved.