Answer first: do not choose a leisure battery from amp-hours alone. Build a 24-hour energy budget in watt-hours, decide how many low-charge days you need, apply the battery maker’s usable-capacity and temperature limits, and confirm that alternator, mains and solar chargers all support the exact battery chemistry and bank size.
Measure the trip you actually take
List every 12V load and every device powered through an inverter. For each, record watts and realistic hours per day. For cycling equipment such as a fridge or heater fan, use measured daily consumption or the manufacturer’s energy figure rather than multiplying its maximum wattage by 24 hours.
| Load | Power | Daily use | Daily energy |
|---|---|---|---|
| Example lights | 12 W | 4 h | 48 Wh |
| Example device charging | 45 W | 2 h | 90 Wh |
| Example fridge | Use measured/day figure | One day | Enter measured Wh |
| Controls and standby | Measure combined draw | 24 h | Watts × 24 |
Add the row totals, then allow for conversion and wiring losses using figures appropriate to the actual equipment. A kettle, hairdryer or induction hob can also impose a high short-duration current even when its daily energy looks modest. Battery, inverter, fuse and cable design must satisfy both energy and peak-current requirements.
Convert capacity into one common unit
For a nominal 12V system, a rough comparison is watt-hours = amp-hours × nominal voltage. Thus a label of 100Ah at 12V describes about 1,200Wh of nominal energy, not automatically 1,200Wh available to loads. The battery manufacturer’s permitted depth of discharge, discharge rate, age, temperature and battery-management limits determine usable energy.
Use this planning sequence:
- Total the expected daily energy in Wh.
- Multiply by the required days without dependable charging.
- Add documented system losses and a realistic operating reserve.
- Divide by the manufacturer’s permitted usable fraction for the chosen battery.
- Check physical size, weight, restraint, terminals, venting and working temperature.
This produces a specification to verify, not permission to install. If the required bank is too large or heavy, reduce loads, change how energy is supplied, or reduce the autonomy target.
Compare specifications, not slogans
| Question | Why it matters |
|---|---|
| What chemistry and construction? | Controls charge profile, usable capacity, venting and temperature behaviour. |
| What cycle-life test conditions? | A cycle claim is meaningful only with its depth, rate and temperature. |
| What continuous and surge current? | Must support inverter and other peak loads. |
| What low-temperature restrictions? | Some batteries restrict charging or discharge outside a defined range. |
| What warranty and installation rules? | Orientation, location, charger or parallel-bank rules may be conditions. |
Yuasa distinguishes leisure batteries by intended use, watt-hours, capacity and cyclic life, and notes that conventional and EFB types require a vented locker or vent pipe while AGM construction differs. That is manufacturer-specific guidance, not a universal comparison of every product. Obtain the data sheet for the exact battery being considered.
Audit every way energy enters the bank
Record the mains charger, alternator arrangement or DC-DC charger, solar controller and any portable supply. For each, capture make, model, maximum current, voltage settings, temperature sensing and supported battery types. An older converter may not suit a replacement chemistry. Alternator and starter-battery protection also need assessment, especially where charging architecture has been modified.
The generation plan must match the consumption plan. Solar depends on season and parking; alternator charging depends on driving; hook-up depends on campsite access. Use the campervan solar guide for Ireland to test one part of the charging case, then model a low-generation day rather than the best summer day.
Prepare a one-page installer brief
- Vehicle, model year and current electrical diagram.
- Daily Wh table, peak AC and DC loads, and autonomy target.
- Existing battery, chargers, alternator, solar, inverter and cable routes.
- Proposed chemistry, capacity, mounting position and environmental limits.
- Required isolation, overcurrent protection, earthing/bonding, monitoring and labels.
- Commissioning tests, manuals, fuse schedule and as-built diagram to be handed over.
Do not copy a fuse or cable size from a generic online diagram. Cable length, installation method, current, fault protection and equipment instructions all matter. Electrical faults can cause fire, shock or equipment damage; use competent help for design and installation.
Checked 24 August 2026 against Yuasa’s leisure-battery selection guidance and Victron Energy’s RV energy and solar sizing method. This page explains planning inputs; it is not an electrical design, installation instruction or product recommendation.