Josh may know the battery as "two for $37.50" but we don't... The battery type will make a difference to the answer.

Hi Mel. I'm not sure which batteries we are talking about. Can you tell me which ones?

If you're talking about lipo or Li-On (3 x 3.7V cells)... I hope you're using a lipo/Li-On charger and a charge control/protection circuit... Continuing to hammer a charge (overcharging) into these types of batteries without overcharge protection won't be a good thing...

No Josh, they are the 12volt ones that they were two for $37.50 and you gave us a 10% discount code and those batteries seem to last forever on a single charge.

You know the ones POWER something or other.

Who is they and who are us? Where di you buy them from? Can you be more specific? What type chemistry are they? Lead acid, NiMH, NiCad, LiPo or Li-On? We need to know this so we can tell you their max charge... They are all different...

Those would be the Sealed Lead Acid (SLA).

Typically, this should be charged at over 12v, common voltage is around 14v, then drops if it's a trickle charger.

When fully charged the battery voltage should be 12.7v

You haven't said if that voltage is while charging, charger voltage or battery voltage after charge. What voltage is the charger? i.e. what voltage is reported on the charger if you have no battery connected? What voltage are the batteries when you take them off charge?

Ah , POWERSONIC , 12v 9ah batteries . I get 12.6 volts when I check mine with a meter after sitting for a while and some use. They may vary depending on charger used and what charge level they are at.

Here's some more info on SLA batteries and charging them, charge levels etc.

Josh guessed the battery. POWERSONIC. Now, I seemed to be only able to get 12.2 with 3 hooked up to the charger.

How long have they been on charge?

What charger and rate are you using?

10A for two days and nights. Three batteries in PAR. It is an automobile charger. I also have a motorcycle charger, but it is only 1.5A. Also, I can put the car charger on 2A.

Try charging them one at a time and see what the voltages are after a good charge (couple of hours should do it depending on how the charger works).

FYI Powersonic is a brand name of SLA battery, they will have the same characteristics as any other SLA battery. The information on the page I linked to earlier will apply to all Lead Acid batteries, it's worth reading.

Mini Factoids from Riches link...   Nearly all batteries will not reach full capacity until cycled 10-30 times. A brand new battery will have a capacity of about 5-10% less than the rated capacity.  Batteries should be watered after charging unless the plates are exposed, then add just enough water to cover the plates. After a full charge, the water level should be even in all cells and usually 1/4" to 1/2" below the bottom of the fill well in the cell (depends on battery size and type).

@Mel , we were having a discussion about batteries balancing the voltage. When in parallel one battery could have a slightly different voltage than the others. This has to do with the resistance of the individual battery and that each battery will be slightly different. Do not use the 10amp charger on one battery . Use the 2 amp. The recommends for best efficiency to limit current to 2.7 amps.

Sidenote : lookup the specs on your 10 amp charger and make sure it keeps up high enough voltage to fully charge these batteries. Specs say this battery needs 14.4 to 14.7 volts from a charger.