I hope this post is not completely off topic here. But because I install UPS's to regulate and supply backup AC power electronic equipment, perhaps you will let this one slip on in. Here goes. . .
The typical lead-acid battery in most of the *smaller* 120v AC switching UPS's is commonly rated 12v 7Ah, 12v 8Ah or 12v 10Ah. Some of them are 6v, but most of them are 12v.
One UPS manufacturer decided to make purchasing "off the shelf" a little more challenging by using a not-so-standard 12v 9Ah battery. Note the *9Ah* mentioned here.
My thinking is that in non-critical runtime environments, I can just use a commonly available 12v *8Ah* battery and all I will lose is a little runtime when the UPS goes "on battery" (compared to the 12v 9Ah battery). I'm not certain how much runtime would be lost, but my guesstimate would be that if a 12v 9Ah battery would typically run a piece of equipment for 20 minutes, perhaps the 8Ah battery would run that same equipment for 15 minutes.
My thinking is also not to use a 12v 10Ah battery, because perhpas the charging circuity was not designed to handle charging a higher capacity battery, or perhaps it would just take much longer time to recharge the battery when the power does come back on. I would primarilty be concerned about overloading the charing circuitry.
I will greatly appreciate any commments, criticisms or suggestions that you may have on this topic.