A bit of battery test
A 12V 100Ah sealed battery from a few years ago has been collecting dust on the shelf for quite a while. Lately I tried to bring it back to life if possible for proper future use.Since I got a brand new 12V Gel battery which has similar capacity as the old one, got them hooked up in parallel to bring up the voltage and get some power in.
Existing capacity
By using a few simple tools (current clamps and voltage meter), a very rough load test was done: running a few relatively constant loads of electronic devices totaling ~100W on the battery through an inverter. AC current measured at ~0.81A (x10 on the AC meter), DC current measured at ~9.3A (x0.1 on the channel) at the start. The testing points during discharging were captured manually.
Discharge data for the new battery
Discharge data for the old battery
Based on the above, the old battery has only ~25% rated capacity left. Common practice for battery usage is to keep the DoD <=50%. Good maintenance practice according to vendor recommendation is a key too. Additional reading for state of charge estimation is at [1].