What Size Victron Battery Charger Do I Need? Amps per Ah

What size Victron battery charger you need comes down to your battery’s amp-hour capacity, its chemistry and how fast you want it full. Victron’s Blue Smart chargers cover almost everything: the IP65 in 12V 4, 5, 7, 10, 15 and 25A (24V 5, 8 and 13A) and the IP22 in 12V 15, 20 and 30A with one or three outputs. Here’s the simple math to choose.

Mobile Solar Consulting compares three Blue Smart chargers.

What Size Victron Battery Charger: The Math

Charge time ≈ amp-hours to replace ÷ charger amps. A 100Ah battery that’s half empty needs about 50Ah: roughly 5 hours at 10A or about 3.3 hours at 15A. Estimate; the final top-off stage is slower, especially for lead-acid.

Commonly cited rules of thumb (estimates, not Victron specifications):

Lead-acid/AGM: around 10–20% of capacity in amps.
LiFePO4: can usually accept more; check your battery’s maximum charge current.

Model Table

Range	12V currents	24V currents	Outputs	Rating
Blue Smart IP65	4, 5, 7, 10, 15, 25A	5, 8, 13A	1	Water and dust resistant
Blue Smart IP22 (120V)	15, 20, 30A	8, 12, 16A	1 or 3	Indoor

Source: Victron Blue Smart IP65 product page and IP22 120V datasheet. The IP22 NIGHT/LOW mode halves current (e.g. 30A to 15A).

Examples (Estimates)

Battery	Suggested charger
Motorcycle or small lithium (under 30Ah)	IP65 12/4 or 12/5
100Ah AGM in a boat or trailer	IP65 12/10 or 12/15
100–200Ah LiFePO4	IP65 12/15, IP65 12/25 or IP22 12/20
300Ah+ house bank	IP22 12/30, or a MultiPlus charger
Two or three separate batteries	IP22 3-output model

Features That Matter

All Blue Smart chargers have Bluetooth via VictronConnect, a lithium mode and a storage mode. The IP65 can act as a power supply. Commenters on charger videos value the storage mode for seasonal vehicles.

For the complete spec sheet and current manual, see the Victron Blue Smart IP65 charger page.

Victron’s Blue Smart IP22 charger product page has the full datasheet and manual downloads.

Worked Example: Overnight Charging

Many owners want the battery full by morning. Working back from an 8-hour window:

Battery and depth of discharge	Ah to replace	Charger for ~8 hours (estimate)
50Ah AGM, 50% empty	25Ah	IP65 12/4 or 12/5
100Ah AGM, 50% empty	50Ah	IP65 12/7 or 12/10
100Ah LiFePO4, 80% empty	80Ah	IP65 12/10 or 12/15
200Ah LiFePO4, 80% empty	160Ah	IP65 12/25 or IP22 12/20
400Ah LiFePO4, 80% empty	320Ah	IP22 12/30 plus longer time, or a MultiPlus

Estimates: Ah ÷ hours, rounded up to the next model. Lead-acid needs extra absorption time at the end, so allow longer than the bulk math suggests.

Worked Example: Two Batteries, One Charger

A boat with a 100Ah AGM house battery and a 70Ah starter battery could use a 3-output IP22 12/20. All outputs share the 20A, so when both batteries are low the current splits between them; as the starter fills, more goes to the house battery. A full recharge of about 85Ah total takes roughly 4–5 hours plus absorption (estimate).

Seasonal Storage

For an RV, boat or classic car parked for months, a smaller charger is often the better choice. Storage mode holds the battery at a reduced voltage, and a weekly refresh cycle tops up lead-acid batteries. A 12/5 or 12/7 IP65 is enough to maintain most single batteries indefinitely.

How to Set Up a Blue Smart Charger

Connect the charger to the battery: positive first, then negative (or to the chassis, away from the battery, on a vehicle).
Plug it into the wall. The charger starts in the last mode it used.
Open VictronConnect, pair over Bluetooth and choose Normal, High or Li-ion mode to suit your battery’s datasheet.
Turn on low current mode for small batteries.
Check the stage indicator: bulk, absorption, float, storage.

Charge Voltages by Mode (12V)

Mode	Absorption	Float	Storage
Normal	14.4V	13.8V	13.2V
High	14.7V	13.8V	13.2V
Li-ion	14.2V	13.5V	13.5V

From the Blue Smart IP22 manual; check your model’s manual.

Worked Example: A Lead-Acid Starter Battery

A car battery of about 60Ah that has gone flat over winter might need around 40Ah replaced. At the 10–20% rule of thumb, a 6–12A charger fits, so an IP65 12/7 or 12/10 brings it back in roughly 4–6 hours plus absorption (estimate). After that, leave it connected: the charger drops to float, then storage, and refreshes the battery weekly.

Temperature and Charging

Lithium batteries generally shouldn’t be charged below freezing unless they have built-in heating, and lead-acid batteries need slightly higher voltage in the cold. If your charger is part of a VE.Smart network with a Smart Battery Sense, it can use the real battery temperature to adjust.

When to Step Up to an Inverter/Charger

If your house bank is 400Ah or larger, or you want shore power to run AC loads as well, an inverter/charger such as a MultiPlus-II charges at up to 120A on 12V. That’s far more than any Blue Smart charger, and it doubles as your inverter.

FAQ

Can a charger be too big for my battery?

Yes, if it exceeds the battery maker’s maximum charge current. Use the IP22’s low mode or a smaller model.

IP22 or IP65?

IP65 for wet or outdoor locations; IP22 for dry interiors, higher current and multiple outputs.

Does the Blue Smart charge LiFePO4?

Yes, there’s a dedicated lithium profile (14.2V absorption on the IP22).

Can I charge a 24V bank with a 12V charger?

No. Use a 24V model, such as the IP65 24/8 or the IP22 24/16.

Is faster always better for lithium?

Not always. Charging below the battery maker’s maximum current is gentler, and a moderate charger is plenty for overnight top-ups.

Can I leave a Blue Smart charger connected all the time?

Yes. That’s what storage mode is for.

Sources: Victron Blue Smart IP65 product page and Blue Smart IP22 120V datasheet (victronenergy.com); Mobile Solar Consulting, “WATCH THIS Before Buying a Victron Blue Smart Charger”; Blue Marine Power, “Blue Smart Charger Guide: IP22 vs IP65 vs IP67”.