Trojan T-105 6V GC2

6 V flooded deep-cycle lead-acid battery in the GC2 golf-cart case: three cells, 225 Ah at the 20-hour rate, 62 lb (28 kg), 10.30 × 7.13 × 11.15 in (262 × 181 × 283 mm). Rated capacity moves with how hard it is pulled — 250 Ah over 100 hours, 225 over 20, 207 over 10, 185 over 5 — and reserve capacity is 447 minutes at 25 A. On a 12 V system it only ever appears in pairs.

Two batteries make the 12 V bank: a jumper from the positive post of one to the negative post of the other, and the two posts left free become the bank's positive and negative. Series does not add capacity — Trojan's own worked example is two T-105s at 12 V and 225 Ah. Four, wired as two series pairs and then paralleled, give 12 V and 450 Ah. The user's guide caps a bank at three parallel strings, and prefers all series cables the same length as each other and all parallel cables the same length as each other.

The series jumper carries the whole bank's current, so it is sized like the main feed rather than like a short link. Chargers, inverters and the distribution feed all land on those two free posts — not across one 6 V battery.

Terminal hardware depends on which of the four versions the battery came with. The stud types (ELPT, EHPT, EUT) take a 5/16" bolt and torque to 95–105 in-lb (11–12 Nm); the automotive post (EAPT) torques to 50–70 in-lb (5.6–7.9 Nm). The user's guide is specific about the stack-up: the cable lug has to contact the lead surface of the terminal, with the washer on top of the lug. A washer between terminal and lug "will create high resistance and cause excessive heating of the connection and terminal".

At 25 °C the datasheet asks a 12 V system for 14.82 V bulk, 13.50 V float and 16.20 V equalize, shifted 0.005 V per cell for every 1 °C away from 25 °C — a series pair is six cells. The user's guide puts bulk current at 10–13 % of the 20-hour capacity, and series does not raise that capacity, so a pair still wants 22.5–29.3 A. Physically it is vented and wet: the datasheet bars installing or charging it in a sealed or non-ventilated compartment and asks 0.5 in (12.7 mm) minimum spacing between cases, and the guide requires it be mounted upright at all times. Terminal height is 1.22 in (31 mm) on the low-profile embedded terminal and 1.50 in (38 mm) on the high-profile one.

Leaving the charger on a generic deep-cycle preset instead of the numbers Trojan publishes for this battery. Trojan's FAQ lists undercharging first under the common mistakes made by flooded battery owners: running a battery continually in a partial state of charge, or storing it discharged, grows lead sulfate on the plates, and "both of these conditions reduce the battery's performance and may cause premature battery failure" — undercharging also stratifies the acid. For a T-105 pair the settings that avoid that are the datasheet's own 14.82 V bulk, 13.50 V float and 16.20 V equalize, which is how one charge-controller thread settles the same question. Watering has the trap in reverse — top up after a full charge, because "watering the battery before charging may result in electrolyte overflow".

• Series jumper sized for the full bank current, cut to the same length as every other series cable in the bank
• A charge source that will hold 14.82 V bulk and 16.20 V equalize on a 12 V pair, with temperature compensation
• A main fuse for the bank's positive feed
• 5/16" hardware and lugs matched to the terminal version, plus terminal protector spray after torquing
• Distilled or deionized water and a hydrometer — the datasheet's state-of-charge table reads either specific gravity or open-circuit volts, 6.37 V full and 6.05 V at half