Batteries Part 2 – Battery Markings

Example:- A particular lithium based battery is branded with the following markings:- 3S, 5000mAh, 25C

Designation:- 3S indicates that the battery is composed of one string of THREE cells in SERIES.

As there is no ‘P’  in the designation (e.g. 3S2P) there is only one string of 3 cells in series. (P is parallel strings)

5000mAh is the NOMINAL CAPACITY of the battery. (Remember we can only safely use 80% of the nominal capacity)

The ‘C’ rating represents the rate at which level the battery is providing energy. (e.g.  higher power with a higher discharge rate (C-rate)).

1C means that the battery is fully charged and discharged within one hour. In our example the battery is branded 5000mAh. 5000mAh may be expressed as 5Ah (5 amps for 1 hour!)  The 1 hour rate is the 1C rating for the battery.

Unless expressly stated on the battery (e.g. Charge at 2C), we should charge the battery at 0.8 to 1C maximum charge rate. As previously shown, for a 5000mAh battery we would charge at 5A MAXIMUM CHARGER CURRENT!

2C is the 30 minute rate (10A), 10C is the 6min rate (50A), 100Cis the 6 second rate(500A)

The final designation on our example battery is 25C. This is the MAXIMUM DISCHARGE RATE that THIS PARTICULAR BATTERY can be charged at. Do NOT exceed this discharge rate in use.

Should a battery become suspect the following actions will provide (if it is actually possible) the best opportunity for ‘recovery’ of the battery.

The battery should be connected to a data logger to record battery terminal voltage and charging current against time:

1. Charge the battery at 1C or less. Ensure the battery is as fully charged as possible.
2. After allowing the battery to rest for approximately 30 minuets, discharge the battery at the 1C rate until approximately 50% of the usable capacity has been extracted. 3.Recharge the battery at the 1C rate.

This charge/discharge cycle should be repeated five times.

The battery should now be discharged at the 1C rate for the full usable capacity of the battery and the result compared with the manufacturers data for the battery. If the measured usable capacity is above 80% of the predicted usable capacity for the battery, (and no other detrimental signs are evident, such as heating or bloating), then the battery may be returned to service.

This procedure is designed to cause a significant portion of the active material in the battery to change state.

For each of the following examples determine:

1. The nominal capacity of the battery
2. The 1C rating for this battery
3. The charging current for this battery
4. The safe maximum instantaneous current this battery is capable of
5. Any special conditions attached to this battery

(There are THREE examples to work through.)