Battery charging

How to charge - when to charge table

Batteries are ready to work in an instant (provided they are charged) and can be used in a reasonably wide temperature range. Charging, on the other hand, has limitations and the user should follow recommended guidelines on how and when to charge. Each battery chemistry has its own charging preference.

Batteries behave like humans; some live to a great old age, others die early. Exposure to heat is likely the biggest enemy. Steps can be taken to prolong battery life but an ideal world will not be possible. The table below provides basic instruction in maximizing battery performance from cradle to grave.

Nickel-based (NiCd and NiMH)
Lithium-ion (Li-ion)
Lead-acid (Sealed or flooded)
How should I prepare my new battery.

Nickel-based batteries come partially charged. Prime new battery by putting on a 14-16h charge.Li-ion comes partially charged. You can use the battery right away and charge it when needed. Lead acid comes fully charged. For best result, apply a topping charge to assure full charge.
Can I damage my battery if incorrectly prepared.No; without priming, the performance will be low at first, then gradually improve with use.No; Li-ion is forgiving to partial and full charge. No priming is needed when new. Lead acid needs a fully saturated charge to keep good performance. A charge can take over 10h.
How do I prepare a battery with charge indication.Fully charge and discharge battery. Repeat when readings get inaccurate.Fully charge and discharge battery. Repeat when readings get inaccurate.Larger lead acid use different charge indicator to nickel & lithium-based chemistries.
Should I use up all battery energy before charging.Yes, fully discharge once every 1-3 months to prevent memory. It is not necessary to deplete the battery before each charge. Over cycling wears down NiMH.No, it is better to recharge more often; avoid frequent full discharges.
Yes, on batteries with a fuel gauge, allow a full discharge once a month to enable reset
No, it is better to recharge more often; avoid frequent full discharges. Deep cycles wear down the battery. Use a larger battery if full cycles are required.
Should I charge my battery partially or fully. Allow full charge without interruptions. Repeated partial charge can cause heat buildup. (Many chargers terminate charge by heat. A fully charged battery will re-heat, causing overcharge.) Does not matter. Charging in stages is acceptable. Full charge termination occurs by reading the voltage level and charge current. Charging a full battery is safe and does not cause harm. Does not matter. Charging in stages is acceptable. Full charge termination occurs by reading the voltage level and charge current. Charging a full battery is safe and does not cause harm.
- Should I remove the battery from the charger when full.
- Should I remove the AC when my laptop is not in use.
Yes, it is best to remove the pack from the charger when full. A prolonged trickle charge to a fully charged battery can be harmful. (Laptops use Lithium-ion)It does not matter. The charger automatically cuts the charge current when the battery is full. A laptop may be connected to the AC when not in use.A float charge of about 2.27V/cell is advisable. Do not allow the open cell voltage to drop below 2.10V/cell while in storage.(Not used for laptops)
Should the battery be kept charged when not in use.Not critical. Manufacturers recommend a 40% charge for long storage. (Open terminal voltage cannot determine state-of-charge.) Store in a cool place. Battery can be fully depleted and recharged. Priming may be needed.Best to store at 40% charge or 3.75-3.80V/cell open terminal. Cool storage is more important than state-of-charge. Do not fully deplete battery because Li-ion may turn off its protection circuit. IMPORTANT: always keep battery fully charged. A discharged battery causes sulfation (insulating layer in the cell). This condition is often irreversible.
Will the battery heat up during charge.Yes, towards full charge. The battery must cool down when ready. Discontinue using a charger that keeps the battery warm on standby. No, little heating is generated during charge. A large laptop battery may get lukewarm. Do not allow the battery to heat during charge.No, the battery should remain cool or lukewarm to the touch. The battery must remain cold on maintenance charge.
What are the allowable charging temperatures.Important: Rechargeable batteries can be used under a wide temperature range.
This does not automatically permit charging at these extreme conditions.
The maximum allowable charge temperatures are shown below:
Slow charge (0.1)
Fast charge (0.5-1C)
0.C - 45.C (32.F - 113.F)
5.C - 45.C (41.F - 113.F)
Charging a hot battery decreases the charge time. The battery may not fully charge.
0.C - 45.C (32.F - 113.F) 5C. - 45.C (41.F - 113.F)
Temperature sensor may prevent charge or cut off the charge prematurely.
0.C - 45.C (32.F - 113.F)
5C. - 45.C (41.F - 113.F)
Warm temperature lowers the battery voltage. Serious overcharge occurs if the cut-off voltage is not reached.
What should I know about chargers.Best results are achieved with a fast-charger that terminates the charge by other than temperature alone. Fastest full-charge time: Slightly over 1 hour.Charger should apply full charge. Avoid economy chargers that advertise one-hours charge. Fastest full-charge time: 2-3 hours.Multi-level charges shorten charge time. Charge must be fully saturated. Failing to do so will gradually decrease the capacity. Fastest full-charge time: 8-14 hours.

Created: May 2003, last edited September 2005

About the Author
Isidor Buchmann is the founder and CEO of Cadex Electronics Inc., in Vancouver BC.
Mr. Buchmann has a background in radio communications and has studied the behavior of rechargeable batteries in practical, everyday applications for two decades. Award winning author of many articles and books on batteries, Mr. Buchmann has delivered technical papers around the world.
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