Sealed Lead Acid Batteries: 12v 7ah; belongs in a Liftmaster LA400 gate control box. Can these batteries be charged using a trickle charger? I'm trying to find out if it's the battery not holding a charge or if it's a bad gate control board. It has 4.85v reading now. If it charges to 8 or so in a few hours, should it hold the charge of 8 with nothing draining it? The battery is on a work bench at the present time and not installed.

fuses good.?
use a voltmeter yet, see if the battery voltage falls like rock even with it turned on and the battery terms drop from
12.6v to way way less is bad battery or charger dead.
to learn which?, then out comes battery and we use stand alone charger to test it. any 12v 1 to 5 amp charger works.
or just replace the battery.
it takes 8 hours for this SPEAKER amp to self charge its battery.

the battery is super common.
12V, 7AH, Lead Acid - 5.94" x 2.57" x 3.78" (L x W x H)

if not kept charged all the time the lead plats sulfate and will not charger, and in most cases fools any device tilling you it is charged
but not me, as I know how to test any battery.

http://www.atbatt.com carries a large array of sealed lead acid batteries. I did a search for 12V 2.8ah and here is one of the results:

http://www.atbatt.com/sealed-lead-acid-batteries/b/interstate/m/interstate-12v-2-8ah.asp

This battery should work -
12 Volt 7 Amp Sealed Lead Acid Battery

It is a 12 volt , 7 ah battery rated at 20 hr. Here is what the 20 hr actually mean -
What does 20 HR mean?

Yes, But. 2 pack so 6volt each, I will assume standard lead acid batteries as the is common, and that is what the pic shows. depends on what you call standard charger, I would not do it with my 40 year old standard charger, although at a push, it will still charge them, but need to keep a check on them, later chargers, monitor the battery voltage, and adjust output to suit. All chargers work the same way, so basically yes, but keep a check on them, not running to hot etc. check voltage if you can. But they all work the same way, just later cells are used to the controlled cct of later chargers. especially with them being so called sealed, they still let gas escape, via a pin hole, If they get hot, to much gas, going out, reduces the effiency of the electrolyte, so will reduce the life, BUT as long as you keep checking them and stop if they get hot no problem, they will get warm anyway.

Just hook these up to a car battery charger. If you need to buy one you can get these at Walmart, Target, CARQUEST, Sears, Napa and many other places similar.

After opening the unit up, this info I found out about the rechargeable battery.
*GS Rechargeable Lead-acid Battery (Portalac) PE12V7A (12v 7Ah) - sealed lead battery*

I hope that info help you, or someone, if you got a 12v 7AMP tip positive DC wall adapter, that thearadacly(sp?) will charge the battery, but I'm doing guess work since I don't know much about the AMP in voltage stuff.

I tried my best.

Yes you can charge the 12 volt bttery on a trickle charger. You should use a 1 amp or less charger. Check the battery every 1/2 hour or so for heat. If it get's hot you should stop charging. Power packs that have a 12 volt rating will charge your battery safer and better but will take longer (like a cell phone charger) look at the voltage ratings on the charger. You will have to adapt the plug to hook it up and test for correct pos. and negative connections. The 7amp hour batery should be fully charged by a .5 amp (500ma) charger in about 14 hours (multiply the amps times hours of charge and do not go over the 7amp hours of the battery when deciding how long to charge). After charging check voltage, it should be around 12. Let the battery set for a few hours (overnight) and check the voltage again. It should be around 12 still. A fresh charge will usually show a higher reading (called a surface charge) than a battery sitting around. 4.5 v will not operate your device, 9.5 v or higher should.

do you have a voltmeter or multimeter?

The sealed lead acid batteries in them have come down a lot in price now, see here for one on batterytrader, 12v 7ah sealed lead acid battery

Most lead acid batteries can be charged with a boost, this can be 10 AMPs, but normally have a current sense circuit so when the battery reaches it knee it goes into a trickle charge.