Step 6: Power, Batteries and Chargers
12V SLA batteries (also known as "gel cell" or "sealed lead acid") are very convenient for a battery-based sound system. They come in many sizes and are inexpensive. If you need 24V, just get two 12V batteries and wire them in series. SLA batteries are widely used in electric scooters, emergency exit lights, "UPS" computer back-up power supplies, etc.
Free batteries! You can often find SLA batteries free at your local recycle center. I've found that the UPS systems are often disposed while the battery inside them is still in good condition and easily removed.
If you want to just buy a new 12V SLA battery, they run $20 to $45 depending on the size. Amazon.com and batterywholesale.com have many sizes, just search for "12v sealed lead acid battery".
For a TA2024 or TA2020 system, you can also run on 8 or 10 AA batteries. Use rechargeables since it will last 3 to 5 hours. You can get a 10-AA battery holder from mouser.com part number 12BH310.
Capacity: SLA batteries come in a wide range of capacities. For a smaller systems a 4Ah to 8Ah battery is good and will be 3 to 6 pounds in weight. Figure on 1 to 2 hours runtime per Ah with a smaller amp. For a larger system or multiple speakers, you probably want to think about how long you need to run your setup for as compared to any weight consideration. With my setup I have 9Ah batteries for a single TK2050 amp, and 18Ah batteries for a dual-speaker setup, both of those will run for 6 or 8 hours at full volume, all day if i turn it down just a little. A standard car battery is around 50Ah. rechargeable AA's are about 2.5Ah capacity.
Charging: 12V SLA batteries can be charged with a small car battery charger, you can also get small and inexpensive chargers designed specially for them. Many electric scooters run on 12V, 24V or 36V, so conveniently you can find $10 to $15 chargers with all 3 of these voltage choices. You can get these $10 scooter chargers at Amazon, just search for "12V SLA charger" or "24V SLA charger" or "36V SLA charger". They come with a connector that you can just cut off and replace with crimp-terminals.
Weight: gel cells are heavy, but you'll still save a lot of weight compared to a car battery just because your setup is efficient so you won't need as big a battery. A car battery is 40 or 50 lbs, and my gel cell is half that weight and powers an equally loud setup. Lithium packs are the lightest, but much more expensive than SLA. You can get some good big lithium packs from all-battery.com.