How to Match a Charger to Your Battery Chemistry
A charger must match the battery chemistry, or you shorten life or create a hazard. This guide explains the IU and CC-CV charge curves, the float stage, the correct charge current in C and how these factors drive cycle life.
View chargersWhich charge curve suits which battery chemistry?
Every battery chemistry has its own end-of-charge voltage and its own charging method. Lead-acid batteries charge on the IU curve (also IUoU), lithium cells on CC-CV (constant current, then constant voltage). A universal charger without chemistry switching is rarely the right choice.
In CC-CV charging the unit first delivers constant current until the cell reaches its limit voltage, then holds that voltage while the current tapers off. Lead-acid also needs an absorption and float phase, whereas LiFePO4 should not be held on a permanent float charge.
How high should the charge current be?
Charge current is stated as a multiple of capacity (the C-rate). 1 C means a 10 Ah battery is charged at 10 A. A moderate current spares the cells, while too high a current creates heat and speeds up ageing.
- Lead-acid: 0.1 to 0.3 C, and not above 0.25 C continuously in cyclic use.
- Li-Ion: 0.5 to 1 C for long life, fast charging only with suitable cells.
- LiFePO4: up to 1 C is uncritical, many cells allow more for short bursts.
- NiMH: 0.1 C for gentle charging, use delta-peak detection for higher currents.
- Rule of thumb: when in doubt charge slower, it extends cycle life.
What do the float stage and battery life involve?
The float stage holds a full battery at voltage without overcharging. It makes sense for lead-acid, but for lithium the unit should end the charge and only top up when needed. End-of-charge voltage, current and state of charge together determine the achievable cycle count.
Keeping a lithium battery between roughly 20 and 90 percent rather than permanently at 100 percent raises the cycle count considerably. A charger with an adjustable cut-off voltage or a charge timer supports this gentle use.
Frequently asked questions
Can I use a lead-acid charger for a LiFePO4 battery?
Only with limits. Many lead chargers at 14.4 V only part-charge LiFePO4 and hold it at voltage through the float phase, which is unfavourable. A unit with a LiFePO4 program, a 14.6 V cut-off and no permanent float is better.
What does the C-rate mean for charge current?
The C-rate relates current to capacity. 0.5 C on a 20 Ah battery is 10 A. A lower value charges more gently and increases cycle life.
Does a lithium battery need a float charge?
No. Lithium cells age faster when held permanently at full voltage. The charger should end the charge and only top up after the voltage has dropped.
Why does my battery charge poorly in winter?
Below 0 °C lithium must not take full charge current, or lithium plating forms. Good chargers measure temperature and reduce the current or block charging.
Looking for the right charger?
We stock chargers and maintainers for lead-acid, Li-Ion, LiFePO4 and NiMH - with the correct curve and temperature compensation.
Chemistry-correct
Charge programs for lead, Li-Ion, LiFePO4 and NiMH.
Temperature-compensated
Protection against charging in frost or overheating.
Charged safely
Cut-off at end of charge instead of overcharging.
Expert advice
We help with the right curve and charge current.