Can I charge a 12V/4Ah sealed rechargeable battery with a 13.5V/500mA charger? If so, how much time would I need to charge it to 100%? If not, how can I charge the battery?
\$\begingroup\$ What's the capacity of your battery? Or do you mean 4Ah instead of 4A? \$\endgroup\$– user17592May 11, 2013 at 19:47
\$\begingroup\$ I think the OP means 4Ah. It's so annoying like when people say the data rate is 4Mbit or say "3MHz" is "3mhz" (double error) \$\endgroup\$– Andy akaMay 11, 2013 at 19:50
\$\begingroup\$ What battery chemistry? What chemistry is the charger designed for? Do you have datasheets that you can provide for both battery and charger? It's really hard to help you based on the limited information you've provided. \$\endgroup\$– HikeOnPastMay 12, 2013 at 5:16
A lead-acid battery labeled 12V, 4Ah and a lead-acid charger labeled 13.5V, 0.5A can work together, likely. Lead-acid manufacturers prescribe that the battery should not be charged at a rate greater than C/3. A 0.5A charge going into a 4A battery is C/8. Expect that it would charge in 8 hours.
Nevertheless, take precautions. Charge the battery outside at least first few times. Lead-acid batteries (abuse-tolerant that they are) can vent hydrogen when abused.
Further reading: BU-403: Charging Lead Acid
I would scrap the idea of using a recylced charger and just buy a cheap 12v lead acid battery charger. Full voltage on a SLA battery is 13.5v, in case you were wondering.
When fully charged, a lead acid battery has a voltage of 12.6V or so, when charging it's normal for that to hit 13.5V and the final charging stage can hit 14.4V (the higher voltage ensures that the battery is fully charged and helps prevent sulphation)
Using a different charger for what the battery is rated for is generally a bad idea. the battery is designed to be used with a specific charger that is rated for the same voltage and Amp Hours (Ah). You should not use this charger with this battery.