My battery was fully discharged (forgot to turn off headlights for a few hours). The car wouldn't even unlock from the remote.
What should I do after getting a jumpstart?
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It is very important to charge back the battery as soon as possible.
As per how fast does the alternator charge the battery?, it may take as much as 10 hours or more for the battery to be re-charged if it was truly fully discharged (which might not necessarily have been the case in itself, due to the potential Negative surface charge?).
It is much cheaper to do that directly with the electricity than plan an unexpected road trip (and especially if it means extra delay of the battery being left in a partially-charged state, as well as potentially not getting that much alternator capacity left over if you're already using AC, lights, radio, and it's so hot outside that the engine cooling fans have to be running at full-speed, too). As such, the best course of action, bar none, is to purchase something like a 6A or 8A charger, and let it charge the battery overnight for a couple of nights, right away from the first night the battery got discharged. Note that the charger automatically charges the battery at 14.4V (2.4V per cell), but after it determines that it becomes fully charged, then it's supposed to float it at 13.5V or so (2.25V per cell), so, these charges are often designed to be left unattended and for an extended periods of time without ill effects.
Once fully recharged, if it's a maintenance-free flooded lead-acid battery, it's also very important to check the fluid level in the battery.
If the battery has been in service for a couple of years already, this step is highly recommended, especially after a deep discharge. If necessary, peel off the label from the top, revealing the cells. As per how much water can be safely added to a battery?, use protective gloves and eye-protection, unscrew the cap, check fluid level with a flashlight -- it should definitely touch at least one side of the filler tube, or potentially two independent sides of the filler tube, forming an eye-like meniscus. (If it doesn't touch either side, make sure to fill in enough distilled water (use at most 10ml per try) to make sure at least one side of each filler tube has the meniscus present.) But make sure to not overfill, and make sure the battery is fully charged in the first place, prior to adding any water.
I recently had my battery discharge just when the warranty expired; I had been working on the car in the garage for a considerable period of time and was using the 12V outlet to power some tools (and the OBD port for my insurance company's metering device). When I was done my work, the battery would no longer hold a charge, even after boosting.
I took the the battery to the local auto parts store for a free 45-minute rapid-charge (AutoZone is one such company that does this for free). The charger will also run a diagnostic on the battery and determine if the battery is no longer usable, or if it can still operate once charged to capacity.
If the battery is still usable, your alternator will charge the battery after it starts the car, and you have nothing to worry about anymore. If it is no longer usable, check to see if electrolyte and/or water can be added to the battery to boost its capacity. If the battery isn't serviceable, you will likely need a new battery.
I'm sure someone has figured out how to service non-serviceable batteries, but I'll leave that up to you to determine if is worth your time and if it meets your risk tolerance level :)