GC2 Batteries on Boats: 6V Golf-Cart Size Explained
GC2 batteries started in golf carts, but they’ve become a favorite for boat house banks. Their thick plates handle daily deep cycling, they’re widely available, and a pair wired in series makes a strong 12V bank. This guide explains GC2 and GC2H sizes, the 6V and 12V options in our store, and how to use them on a boat. Check product pages for exact dimensions and current specs.
What GC2 means
GC2 is a BCI group size for golf-cart batteries. Typical dimensions are about 10.3 inches long, 7.1 inches wide and 10.9 inches high, so a GC2 is about the same length as a group 24 but wider and noticeably taller. GC2H is a taller version, which leaves room for more plate area and capacity. Always check the exact height on the listing, because the extra height is often what decides whether a battery fits.
Most GC2 batteries are 6V. To make 12V, wire two in series. Some lithium makers now build 12V batteries in a GC2 case, so one battery delivers 12V in the same footprint.
6V GC2 options in our store
| Model | Type | Capacity (20-hr) | Reserve @ 25A | Weight | Case |
|---|---|---|---|---|---|
| Trojan T-605 | Flooded | 210Ah | 383 min | 58 lb | GC2 |
| Trojan T-105 / T-105 Plus | Flooded | 225Ah | 447 min | 62 lb | GC2 |
| Trojan T-125 / T-125 Plus | Flooded | 240Ah | 488 min | 66 lb | GC2 |
| Trojan T-145 / T-145 Plus | Flooded | 260Ah | 530 min | 72 lb | GC2H |
| Trojan T105 AES | AGM | 240Ah | 529 min | 89 lb | GC2 |
12V lithium in a GC2 case
| Model | Capacity | Weight | Notes |
|---|---|---|---|
| Battle Born 100Ah GC2 | 100Ah at 12V | 31 lb | Lists 3,000–5,000 cycles, 100% usable depth of discharge |
Battle Born also makes a 270Ah 12V GC3 battery at 80.8 pounds for larger golf-cart-style spaces.
Why boaters choose GC2 banks
- Durable cycling. Golf-cart batteries are designed for deep discharge every day. They usually outlast 12V marine deep-cycle batteries in house-bank use.
- Capacity. A pair of T-105s gives 225Ah at 12V, more than two group 27 batteries in parallel.
- Value. Flooded GC2 batteries are among the lowest-cost ways to get a lot of amp-hours.
- Availability. The size is common, making replacements easier.
The downsides
- Weight. A pair weighs 116–144 pounds in flooded form.
- Height. GC2 batteries are tall, and GC2H taller still. Many boat battery boxes can’t fit them.
- Watering. Flooded models need regular distilled water.
- Ventilation. Flooded batteries vent hydrogen while charging, so the compartment must be ventilated.
- Two batteries per 12V. If one fails, you generally replace both.
Wiring a 6V pair to 12V
Connect the positive terminal of one battery to the negative of the other. The remaining negative and positive terminals become the bank’s 12V outputs. For a larger bank, wire two pairs in series, then connect the pairs in parallel. Take the main positive from one end of the bank and the main negative from the other to balance current between pairs. Fuse the main positive close to the battery.
Usable capacity
Flooded GC2 batteries should be cycled to about 50% for good life. A T-105 pair gives about 112Ah usable at 12V; a T-145 pair about 130Ah. A single Battle Born GC2 gives close to its full 100Ah, so one lithium battery roughly matches a 6V pair’s usable energy, at a quarter of the weight. Two Battle Born GC2s in parallel nearly double it.
Maintenance for flooded GC2 batteries
- Check electrolyte levels monthly, more often in hot weather or with heavy use.
- Add distilled water after charging, to just cover the plates or to the level the maker specifies.
- Keep tops clean and dry to prevent self-discharge across the case.
- Tighten terminals and jumpers; loose jumpers cause heat and voltage loss.
- Follow Trojan’s guidance on equalizing, and only equalize flooded batteries.
A single-point watering kit can make this much easier in tight lockers.
Charging
Use a multi-stage charger with a flooded profile, or AGM for the T105 AES. Golf-cart batteries prefer a full charge after every use; chronic undercharging leads to sulfation and lost capacity. At rest, a fully charged flooded 12V bank reads about 12.6–12.7V, and about 12.2V at 50%.
Is a GC2 bank right for your boat?
| You have… | Consider |
|---|---|
| Tall, roomy battery box, budget priority | Flooded T-105 or T-125 pair |
| Extra height available | T-145 pair for the most capacity |
| Sealed battery needed, no watering | T105 AES pair |
| Weight matters, GC2 trays already installed | Battle Born 100Ah GC2 (one or two) |
| Short battery box | Group 27 or 31 batteries instead |
Mixing old and new
Don’t add a new GC2 battery to an old bank or pair a new battery with an old one in series. The weaker battery drags down the stronger one and both wear out faster. Replace batteries in matched sets of the same model and age.
Warranty
Our Trojan listings and the Battle Born GC2 listing don’t show warranty terms. Check each maker’s terms before buying.
More reading
For Trojan model details, read Trojan T-105 vs T-125 vs T-145, and for lithium GC2 options, see Battle Born GC2 vs group 27/31. For other sizes, see group 27, group 31 and 4D and 8D. Before ordering, measure your battery compartment. The full chart is in BCI battery group sizes explained, and cranking vs dual-purpose vs deep-cycle explains battery types. The marine battery buying guide covers the rest.
Products mentioned
Frequently asked questions
What is a GC2 battery?
A golf-cart battery size, usually 6V, about 10.3 x 7.1 x 10.9 inches. Check listings for exact dimensions.
What’s the difference between GC2 and GC2H?
GC2H is a taller case with room for more capacity, like the Trojan T-145.
Can I use GC2 batteries on a boat?
Yes, as a house bank. Wire two 6V batteries in series for 12V, and ventilate flooded types.
Is there a 12V GC2 battery?
Yes. Battle Born’s 100Ah GC2 is a 12V lithium battery in a GC2 case.
How long do golf-cart batteries last on a boat?
With proper charging and watering, flooded GC2 batteries often last several years in house-bank service.