Decide if you want a "charger" or a "maintainer". Maintainers are not great chargers due to limited current, chargers can be poor maintainers due to a lack of sophisticated voltage control. So if the goal is to connect to a battery indefinitely (standby use) then seek out a maintainer. If the goal is to charge a battery relatively quickly for periodic use, then a charger is what you want. I've bought name brand battery maintainers at Costco for about $30 so I see no need to save $10 on a no name china special with questionable performance. For a small battery even a small maintainer (~2 amp) could also double as a charger, so that might be a good all around solution. A 12Ah "lead acid" battery is almost surely a gel cell so make sure whatever charger or maintainer you get is appropriate for gel batteries. They are very sensitive to charge current rate (check the data sheet).
Mark B.
Albuquerque, NM