Suzuki is a trademark of its owner. Amp Hour Supply isn’t affiliated with Suzuki.
The short answer. The DF300AP has a 54 A alternator and a dual charging system that can feed a second battery on its own circuit, with an optional harness. For a lithium house bank, put a 30 A DC-DC charger between the engine and the bank instead of running lithium straight off that second circuit.
Suzuki’s own figures
From the DF250AP/DF300AP owner’s manual (S1) and Suzuki’s product sheet (S2):
| What | Suzuki says | Where |
|---|---|---|
| Alternator | 12V 54A | S2 p.1 |
| Voltage regulator | Water-cooled | S2 p.4 |
| Starting battery minimum | 1000 MCA, or 800 CCA, or 180 RC minutes, or 130 AH (20HR/IEC) | S1 p.28 |
| Battery type for starting | 12 V starting-type lead acid; no deep cycle, no gel-cell | S1 p.28 |
| Dual battery charging | Optional isolator lead assembly, 40 A fuse moved to OPT | S1 p.30 |
| Sub battery cable fuse | 30 A | S1 p.30 |
| Main fuse / isolator select fuse | 60 A / 40 A | S1 p.75 |
What Suzuki’s dual charging does, and doesn’t
Suzuki is clear about the idea. With the optional harness, the DF300AP charges the main and auxiliary batteries at the same time, on separate circuits. You can run the house battery down and still start the motor.
It was designed around lead-acid. Suzuki’s own battery page calls for a starting-type lead acid battery and recommends an auxiliary battery when the boat has extra loads. It says nothing about lithium.
Put lithium on that auxiliary circuit and the only limit is a 40 A fuse. Lithium will take current until something stops it, and Victron’s Orion-Tr manual says direct charging can overload an alternator. That’s why the bank goes behind a DC-DC charger. The whole comparison is in Charging lithium from a boat alternator: 3 ways compared.
One charger, and where to feed it from
Victron’s manual says an alternator at idle may give about half its rating, and less hot. Half of 54 A is about 27 A. One Orion-Tr 12/12-30 fits that at cruise, and may pause at idle with loads on. Two won’t.
Where you take the input from is a question for your Suzuki dealer, not us. The safe default is the starting battery positive, fused right at the battery. If your boat already has the isolator lead fitted, ask the dealer whether to feed the charger from it or move the 40 A fuse back to standard.
Leave the sub battery cable alone. Suzuki uses it to power the engine control system, on a 30 A fuse, and the engine won’t start if it’s wired wrong.
You’ll need
- Victron Orion-Tr Smart 12/12-30 isolated DC-DC
- Fuses for the charger’s input and output
- Tinned cable from the Wire gauge calculator (Suzuki’s manual gives no cable size, so this is down to the charger’s manual and your run length)
- Victron SmartShunt 500A
- Victron Smart BatteryProtect 100A
Steps
- Engine off. Main switch off.
- Keep a starting battery that meets Suzuki’s minimum. If you run two in parallel for starting, Suzuki wants them the same type, capacity, maker and age.
- Talk to your dealer about the dual charging setup (step above), then mount the charger near the start battery.
- Run and fuse the input.
- Run and fuse the output to the house busbar.
- House negative through the SmartShunt.
- Set your lithium battery maker’s voltages in VictronConnect.
- Sea trial: cruise, then idle, watching the amps. Suzuki warns that heavy accessory use can drain a battery under some conditions, and the SmartShunt shows you when that’s happening.
AC work (shore power, inverter-charger) goes to a licensed electrician.
Fit
Fits: a Suzuki DF300AP or DF250AP covered by owner’s manual 99011-98JF0-03B, on a 12V boat, adding a lithium house bank while keeping a lead-acid start battery.
Doesn’t fit: – Other DF300 versions (DF300B, the older DF300). Their manuals may differ. – Plans to swap the starting battery to lithium. Suzuki’s manual calls for starting-type lead acid. – A house bank whose lithium maker says something different. Their manual wins.
Products
| Product | On a DF300AP |
|---|---|
| Victron Orion-Tr Smart 12/12-30 isolated DC-DC | 30 A into lithium, inside the 54 A alternator. |
| Victron SmartShunt 500A | Shows charge in and loads out. |
| Victron Smart BatteryProtect 100A | Disconnects house loads before the bank runs low. |
| Victron Cyrix-ct 12/24V 120A | Only if you add a lead-acid thruster or windlass battery. |
Prices show live in the store.
Bundles for this job: Dual-battery DC-DC charging kit, Boat lithium upgrade kit, large
Quick answers
What’s the alternator output on a Suzuki DF300AP? Suzuki’s product sheet lists 12V 54A.
Can Suzuki’s dual battery charging feed a lithium bank? It’s built to charge a second battery on its own circuit, protected by a 40 A fuse. For lithium, add a DC-DC charger so the current is capped and the charge profile suits the battery.
Can I start a DF300AP on a deep cycle battery? Suzuki says not to. Use a 12 V starting-type lead acid battery that meets the minimum rating.
Sources
- Suzuki DF250AP/DF300AP Owner’s Manual, 99011-98JF0-03B: https://www.suzukimarine.com/wp-content/uploads/manuals/owner/WEBK24_DF250AP_300AP_99011-98JF0-03B_440001EN-1.pdf
- Suzuki Product Information, DF300AP/250AP Lean Burn: https://assets.suzukimarine.com/wp-content/uploads/2022/06/21102641/Suzuki-DF300AP-DF250AP.pdf
- Victron Orion-Tr Smart DC-DC Charger Isolated manual (Rev 14, 02/2026): https://www.victronenergy.com/upload/documents/Orion-Tr_Smart_DC-DC_Charger_-_Isolated/34439-Orion-Tr_Smart_DC-DC_Charger-pdf-en.pdf
