Glossary

Float charge

Unit V · Also Float, Trickle charge

What is Float charge?

The last phase of a charging process: a reduced continuous voltage that compensates for self-discharge without stressing the battery further.

What matters about Float charge in practice?

For lead-acid batteries it is the normal state on shore power for weeks at a time. The value is typically a few tenths of a volt below the end-of-charge voltage and depends on temperature — which is why a temperature sensor belongs on the battery.

With lithium, permanent float charging at a high level tends to be harmful. Many systems therefore charge to a value and then switch off instead of holding permanently.

Which voltage applies to float charging?

For 12 V lead batteries it is typically around 13.5 to 13.8 V; the exact values are in the data sheet. It is chosen so that the battery stays full without gassing or drying out. It is lowered in warm conditions and raised in the cold.

How do you store a lithium battery over winter?

LiFePO4 batteries are not kept permanently full. Many manufacturers recommend a medium state of charge for storage, often around 50 to 60 percent, and switching off charger and loads. The exact recommendation comes from the manufacturer.

What to do with lead batteries in winter storage?

  • Store them fully charged and recharge regularly, or leave them on a charger with float charging.
  • Open the battery main switch so that no standby current drains the battery.

The page charger and inverter shows suitable chargers with several charging stages.

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