RV Battery Charge Time Calculator: How Long to Full?

Enter your bank capacity, starting charge, target and available charging current. The calculator estimates a constant-current bulk stage followed by an absorption stage at a lower average current. It is a planning model, not a measurement of your battery or a forecast of the charger’s exact termination time.

Set the equipment to respect the battery’s charge-current limit. The calculator caps its arithmetic at your entered limit; a real battery does not necessarily regulate an oversized charger to that value. Account for all simultaneous sources and house loads.

What the calculator is doing

1. Charge to add: capacity × the state-of-charge change. A 200Ah bank going from 20% to 100% needs 160Ah stored.
2. Planned current: the lower of available source current and your allowed bank-current setting. This assumes the real installation enforces the limit.
3. Bulk time: the Ah below the model’s stage transition divided by current and charge efficiency.
4. Absorption time: the remaining Ah divided by an average current of 30% of the bulk value, again allowing for efficiency.

The efficiencies are amp-hour storage assumptions, not AC charger efficiency. The model excludes temperature, house consumption, voltage drop, changing solar output and any fixed absorption or balancing timer in the actual charger.

Two limits to check before choosing a converter

Available source current and allowed battery current are different numbers. Battle Born’s BB10012 manual lists a 50A maximum and 0.5C recommendation. Treat that as a requirement for the charging setup, not evidence that an 80A source will harmlessly self-limit.

For a generic 100Ah lithium example starting at 20%, the model gives:

Current actually configured and available	Estimated time to full
45A	2 hr 3 min
50A	1 hr 51 min

A larger converter needs verified current limiting if its output exceeds the allowed bank current. A suitable charge profile is a separate requirement. The calculator’s product suggestions stay within the entered current allowance; they are not a complete compatibility check.

On a 200Ah bank permitted to charge at 100A, the same model gives 4 hr 7 min at 45A and 2 hr 19 min at 80A. These are conditional calculations, not guaranteed Battle Born charge times. The manufacturer also specifies its own absorption duration, which this generic model does not reproduce.

Why the absorption tail matters

Fixed worked example: 200Ah AGM, 50% to 100%, with 45A available for charging and an allowed bank current of at least 45A. This is not your live result. It uses the calculator’s 85% charge efficiency and 30% average absorption-current assumptions.

1 · Bulk

50% → 80%
60Ah in 1 hr 34 min
45A held constant in the model

2 · Absorption

80% → 100%
40Ah in 3 hr 29 min
13.5A modeled average; actual current tapers

40% of the added Ah, 69% of the modeled time. In real charging, bulk ends when the configured voltage is reached; absorption holds that voltage while current falls. The switch is not triggered by a universal 80% state of charge.

The Victron charge-stage explanation supports the stage sequence, not this example’s fixed duration or 30% averaging factor. Follow your battery and charger’s termination, balancing and storage instructions. This estimate excludes house loads, changing solar output and temperature effects.

Victron’s charger manual describes bulk as maximum-current charging until the configured voltage is reached, then absorption as voltage held while current decreases. State of charge at the transition and absorption duration depend on the system.

The worked example uses 45A, not an unspecified converter. At 80A available but a 50A configured bank limit, this model gives 4 hr 33 min. It shortens both modeled stages because the 30% absorption average scales with bulk current. The earlier claim that a bigger charger could not affect the tail was too absolute. Real charge profiles may instead impose their own duration.

What chemistry changes in this model

Only the 0.5C example above comes from that specific Battle Born instruction; it is not a limit for all lithium batteries. The remaining values are declared planning approximations. Renogy’s 100Ah AGM specifications give a 30A maximum, illustrating why the generic 25A default for 100Ah should not be mistaken for the model’s datasheet.

Recommended current versus maximum current

LiTime’s Group 24 specifications list 20A recommended and 100A maximum charging. With other inputs fixed, our 100Ah lithium example estimates 4 hr 38 min at 20A versus 56 min at 100A. Those times illustrate the model; they do not establish the same cycle life, temperature behavior or suitability at both rates.

Use the exact battery’s instructions and configure the charging system accordingly. A BMS fault cutoff is not a normal current-control strategy.

Charging from multiple sources

The calculator adds checked sources, assuming they are compatible and run steadily. If their combined output exceeds your limit, it warns that the equipment must be limited or coordinated. Extra available current is not automatically rejected harmlessly by the battery.

The solar estimate is watts × 0.75 ÷ 13.6V: about 22A for 400W. It assumes continuous full-sun conditions for that calculation, not all-day availability. Use solar sizing for seasonal energy planning. A DC-DC charger also draws power from the vehicle; alternator charging is not free energy or automatically available at its full label rating.

Checks that change the answer

• Enter total parallel-bank Ah at the system voltage; series strings do not add Ah. Check the permitted current of the actual arrangement.
• Deduct concurrent house loads from available charging current. This tool has no separate load input.
• Verify every source’s current and voltage settings, including simultaneous charging, before using the capped estimate.
• Follow the maker’s absorption, balancing and storage instructions. Reaching the model’s target is not proof that a real battery has completed its cycle.
• Confirm permitted charging temperatures. The estimate has no cold-charge, heating or thermal-derating model.

Converter options to compare

These are starting points for checking output, profile and installation, not universal matches for a particular Ah label.

Related guides

• Best RV converter for lithium batteries — which converters have a real lithium profile, which is a separate question from how fast they charge.
• Do I need a DC-DC charger? — the alternator source, and whether it is worth fitting.
• RV battery calculator — how big the bank needs to be in the first place, and the discharge side of the same numbers.
• Lithium vs AGM for RV — the charging difference on this page is one of the strongest arguments in that comparison.
• 12V wire size calculator — the cable between the charger and the bank, which has to carry every one of these amps.
• Charging lithium in cold weather — the per-brand temperature cutoffs this calculator deliberately does not model.
• The electrical section collects everything published so far.

For how products on this site are selected and what we do not claim about them, see the editorial policy.

Questions worth answering