Lithium vs Lead-Acid Battery Charging
How lithium and lead-acid batteries charge differently: efficiency, safe charging current, charge stages, full charge time and depth of discharge, with 100 Ah examples.
By the ChargingTimeCalculator.com team
Lithium batteries charge faster and waste less energy than lead-acid batteries. A 100 Ah lithium battery can safely take 20 to 50 amps (0.2C to 0.5C), and more than 99% of the charge you put in comes back out. A 100 Ah lead-acid battery usually takes 10 to 30 amps (0.1C to 0.3C) at about 90% efficiency. On a 10 amp charger, lead acid needs 111.1 Ah to go from empty to full, which is about 11 hours 7 minutes before its slow topping stage.
The battery charging time calculator has a battery type setting that applies these differences. Here is what changes and why.
Efficiency: how much charge comes back out
Coulombic efficiency is the share of charge put into a battery that you can take back out. Battery University gives these figures:
| Chemistry | Coulombic efficiency |
|---|---|
| Lithium-ion | Above 99% |
| Lead acid | About 90% |
| NiCd and NiMH | Up to 90% with fast charge, about 70% on slow charge |
For a 100 Ah lead-acid battery, that 10% loss means putting in about 111 Ah to get 100 Ah back. A lithium battery needs only slightly more than 100 Ah.
Charging current and C-rates
The C-rate expresses current as a fraction of capacity. For a 100 Ah battery, 1C is 100 amps and 0.1C is 10 amps. Battery University describes 0.1C as a 10 hour rate and 0.5C as a 2 hour rate.
| Lead acid | Lithium | |
|---|---|---|
| Typical charge rate | 0.1C to 0.3C | 0.2C to 0.5C |
| 100 Ah battery | 10 to 30 A | 20 to 50 A |
Battery University says lead-acid makers recommend 0.3C. For lithium-ion energy cells it gives an advised rate of 0.5C to 1C, with makers recommending 0.8C or less to prolong battery life. Always follow the limits on your battery’s spec sheet. The battery charging current calculator shows the range for your battery’s size and type.
Charge stages compared
Both chemistries start with a constant current stage, then switch to a constant voltage stage where the current tapers. This is called CC-CV charging. The details differ.
Lead acid, per Battery University’s lead acid charging guide:
- Constant current brings the battery to about 70% in 5 to 8 hours.
- The topping charge fills the last 30% over another 7 to 10 hours.
- A float charge then holds the battery at full.
- A full charge takes 12 to 16 hours.
Lithium-ion, per Battery University’s lithium charging guide:
- A high current fills the battery to about 70% quickly.
- State of charge is about 85% when the constant current stage ends.
- The battery is full when the current falls to 3% to 5% of its Ah rating.
- A full charge takes about 2 to 3 hours at 0.5C to 1C.
- No float stage is needed.
The big practical difference is the tail. Lead acid needs its long topping stage to stay healthy, while lithium can stop short of full.
Depth of discharge and usable capacity
Depth of discharge is how much of the battery you use before recharging. It sets how much of the rated capacity you can count on.
The battery runtime calculator assumes lead acid is used to 50% depth of discharge. So a 100 Ah, 12 volt lead-acid battery holds 1,200 Wh but gives you 600 Wh of usable energy, enough to run a 100 watt load for 6 hours.
Lithium can be cycled deeper, but deeper cycles still wear it faster. Battery University’s guide to prolonging lithium batteries estimates an NMC lithium cell lasts about 300 cycles at 100% depth of discharge and about 1,000 cycles at 40%, before its capacity falls to 70%.
Full charges and storage
The two chemistries want opposite things when they sit unused. Lead acid should be kept full. Battery University says one deprived of a full charge will gradually lose capacity through sulfation. Lithium is happier partly charged. The same source estimates that a lithium battery stored a year at 25°C keeps 96% of its capacity at 40% charge, but only 80% at 100% charge.
Phones and power banks
Phones and power banks use lithium cells, so the same rules apply. A 5,000 mAh battery at 3.7 volts holds 18.5 Wh. On a 20 watt charger at 85% efficiency, it takes 21.8 Wh and about 65 minutes before the slow top-off. Phones slow down past about 80%, which matches the taper in the constant voltage stage. See milliamp-hours for the unit, and the car battery charging guide for 12 volt lead-acid details.
Frequently asked questions
Can I charge a lithium battery with a lead-acid charger?
Only if the charger has a lithium setting or the battery maker approves it. The two chemistries use different charge stages and voltages. Battery University notes that lithium-ion cannot absorb overcharge and needs no trickle, float or equalizing charge, all of which lead-acid chargers may apply. Check both manuals first.
Does a lithium battery need to be fully charged?
No. Battery University says lithium-ion does not need a full charge the way lead acid does, and a partial charge is fine. Lead acid, by contrast, slowly loses capacity to sulfation if it is regularly left undercharged.
Why does a lithium battery charge faster?
It accepts more current and loses less energy. Lithium-ion is above 99% coulombic efficient and can take 0.5C to 1C, so a full charge takes about 2 to 3 hours. Lead acid is about 90% efficient and usually takes 12 to 16 hours.