ProMariner ProSportHD chargers for a thruster battery

A dedicated thruster battery only works if something keeps it full. Leave it to the alternator through a combiner and you are back to tangling the thruster with the rest of the electrical system. Our usual answer is a small sealed charger next to the battery, fed from one AC circuit, so the thruster battery tops itself up whenever the boat is plugged in. ProMariner's ProSportHD is the charger we reach for most often in that role.

What it is

The ProSportHD is ProMariner's fourth-generation waterproof onboard charger. It is a sealed box with a pre-wired AC cord and pre-wired, fused DC leads, built to be bolted down in a wet compartment and forgotten. The line runs from the single-bank ProSportHD 6 (6 amps) to the 20-amp, three-bank ProSportHD 20 Plus, with Global versions that accept 100-240V input. It carries a UL Marine 1236 listing, ignition protection and a 3-year warranty.

The lineup, for thruster purposes

Every bank lead must go to a 12V battery, but the manual allows doubling leads onto one battery when there are more outputs than batteries. Combined with ProMariner's Distributed-On-Demand feature, which moves unused amps to whichever bank still needs them, a two-bank charger can put its full output into a single thruster battery.

Sizing it to the battery

This is where most DIY setups go wrong. The ProSportHD is designed for group 24 through 31 batteries. ProMariner's manual says plainly that it is not for 4D and 8D batteries and points to the ProNauticP line for those.

Within group 31, the battery maker's charging rules matter:

• Odyssey Extreme 31M. Odyssey's technical manual says charge current should be at least 40% of the 10-hour rating for best results and never below 10%. With a 98 Ah 10-hour rating, the 6-amp ProSportHD 6 falls under that floor. A ProSportHD 12 with both leads on the battery gets you into acceptable range. Odyssey also wants about 14.7 V absorption, which matches the ProSportHD's AGM profile.
• Lifeline GPL-31T. Lifeline asks for 14.3 V ±0.1 V absorption and 13.3 V float, and at least 0.2C for repeated deep cycling. The ProSportHD AGM profile is 14.7 / 13.6 V, so it runs a little hotter than Lifeline's numbers. A thruster battery that sees short bursts is not deep cycling, but it is worth checking with Lifeline before you commit.

The profile is set with a button on the front during the analyze phase, and it ships set to flooded. Changing it to AGM is the step people forget.

Install notes from the bow locker

• Mounting. ProMariner wants 6 inches of clear space around the charger, a hard surface (no carpet or vinyl) and ventilation. In a tight forward compartment, find that space before you place the battery.
• DC leads. The leads are 6 ft with inline fuses about 4 inches from the battery end. Do not cut them. If you need more reach, ProMariner sells fused 5 ft and 15 ft extenders.
• AC side. The charger plugs into a grounded, GFCI-protected outlet, and the manual wants the AC cord at least 21 inches from the charger, batteries and fuel fills. We run one small dedicated circuit from the AC panel to an outlet in a dry spot near the bow.
• Battery types. ProMariner warns against mixing chemistries on one charger. On a thruster-only charger that is easy, since there is one battery.

24V thruster banks

Larger thrusters often run on 24V, built from two 12V batteries in series. The ProSportHD handles that without rewiring the bank: each charger lead goes to its own 12V battery, and ProMariner's manual says you do not have to remove series or parallel jumpers to use it. A two-bank ProSportHD 12 or 20 on a pair of group 31s is a common, tidy setup for a 24V thruster. The batteries should be the same type and age, which you want in a series pair anyway.

Weak spots

The fixed leads are tidy until they are 18 inches short. The 8D limit rules the ProSportHD out for big 12V thrusters on a single large battery. And because the AGM profile is fixed at 14.7 V absorption, owners with batteries that want a lower setting have to accept a compromise or choose a programmable charger. On lithium, ProMariner's catalog lists approved LiFePO4 support, but older manuals do not mention it, so confirm before you assume.

Alternatives

A combiner or DC-DC charger from the house or engine system can work and saves running AC forward. It also ties the thruster battery back to the systems we were trying to keep it separate from. For big thruster batteries, a larger hardwired charger is the usual step up. For a group 31 thruster battery on a boat that lives on shore power, the ProSportHD is hard to beat for simplicity.

Verdict

The ProSportHD 12 is the sweet spot for a single group 31 AGM thruster battery: enough current to satisfy Odyssey's rules when both leads go to the battery, sealed for the bow, and simple to wire. Skip the 6-amp model on an Odyssey, and skip the line entirely for 8D batteries. Pair it with the battery choices in our AGM thruster battery review, or let us spec the whole package as part of a bow thruster installation.

Questions people ask