AGM or Lithium for a Cruising House Bank? Getting Years from the Batteries You Own

It is the question we get asked more than any other: should the next house bank be AGM again, or is it time for lithium? The honest answer, from a workshop that installs and bench-tests both, is that for most cruising boats in Thai waters a well-cared-for AGM bank remains the sensible choice — and that whichever chemistry you own, the difference between a bank that dies young and one that gives years of service is not the badge on the case. It is how the bank is stored, charged and used. That is what this guide is about.

The habits that decide an AGM bank’s life

An AGM battery is happiest full. Its one genuine dislike is being left partly discharged: a lead-acid battery that sits below full charge slowly sulphates, and sulphation — not age — is what quietly removes capacity from most cruising banks. The working rules are simple. Recharge promptly and fully after use rather than leaving the bank half-done for days. Plan your capacity around a 50% depth of discharge so the bank cycles shallow and lives long — our battery bank calculator sizes this for you in a couple of minutes. And never leave a bank flat: a discharged battery in a hot boat sulphates in weeks, not months.

Charge quality matters as much as charge quantity. Use charger settings taken from the battery’s datasheet rather than a generic “AGM” preset, enable temperature compensation, and mount the temperature sensor on the battery case itself. Our guide to installing AGM batteries in tropical heat covers siting and charge voltages in detail — between them, those two things are most of what decides whether a bank sees two years or five-plus.

Storing AGM batteries: layup and between trips

Storage is where good banks are made or lost in this climate, because self-discharge roughly doubles with every 10°C of temperature. A bank that would hold its charge for six months in a European winter needs attention monthly in a Thai hot season.

• Charge fully before you leave the boat. A full battery resists sulphation; a half-charged one doesn’t.
• Disconnect standing loads. Bilge-pump float switches aside, nothing should be quietly drawing the bank down while you are away. A battery switch left on with a stereo memory wire attached has ended more banks than any manufacturing fault we have seen.
• Keep it cool. A ventilated locker low in the boat over a lazarette under a dark deck, every time. Cool storage halves every ageing process at once.
• Float it or top it up. The ideal is a proper temperature-compensated float charge or a small solar maintainer. Failing that, a full recharge once a month through the hot season keeps the bank healthy.
• Laying up for the monsoon? Follow the battery section of our southwest monsoon layup guide — charge, disconnect, and either float aboard or store ashore somewhere cool.

Using the bank day to day

A few habits in daily use add years. Keep terminals clean, tight and lightly greased — resistance at a terminal makes heat exactly where you don’t want it. If your bank is several batteries in parallel, wire it symmetrically so every battery works equally; our guide to connecting batteries in parallel shows the layouts that share current properly and the ones that quietly overwork one battery. Give the bank air: leave gaps between cases and keep the compartment ventilated. And once or twice a season, rest the bank overnight and check each battery’s voltage individually — a spread of more than 0.1–0.2 V between identical batteries is your earliest warning that one needs attention.

Where lithium genuinely earns its price

Lithium (LiFePO4) is a fine technology, and there are boats where it is the right answer. If you live aboard and cycle the bank deeply every day, lithium’s cycle life and fast charge acceptance repay the premium. If weight matters — a performance catamaran, a tender with a big electric outboard — lithium is transformative. And a lithium bank holds usable voltage across most of its discharge, which big inverter loads appreciate.

Set against that: a lithium installation is only as good as its BMS, balance wiring and terminations, and it usually means new chargers, a DC-DC for the alternator, and careful integration — the true cost is the system, not the cells. There is also a practical Thailand point that surprises people: sealed AGM is classified non-hazardous for transport, so a replacement can be on a courier to a boatyard in Krabi tomorrow, while lithium moves under dangerous-goods rules — our guide to shipping marine batteries explains why that matters when you need a battery now.

The verdict for most boats here

If your boat spends weeks at a time unattended in the heat, sails at weekends, and charges from a mix of solar and engine, a properly sized AGM bank — stored full, kept cool, charged with temperature compensation — is the simple, robust, economical answer, and the storage and use habits above will take it to the far end of its service life. If you live aboard and hammer the bank daily, price lithium honestly as a whole system and it may well earn its keep. Either way, the battery you look after outlasts the battery you don’t, by years.

Where we come in

Drake Marine is a specialist supplier of genuine Fullriver AGM batteries — deep-cycle, engine-start and dual-purpose — stocked in Trang, bench-tested before dispatch, delivered free to Trang, Krabi and Phuket and shipped Thailand-wide and worldwide. We will size a bank with you rather than sell you the biggest one, and if your existing bank just needs better storage habits and a charger setting, we will tell you that instead.

Talk to us at hello@drakemarine.com or through the contact page.