Dual purpose batteries are often used not only as main boat batteries, but also as batteries for golf carts, Recreational Vehicles (RV) batteries, All Terrain Vehicles (ATV) batteries, Uninterruptible Power Supply (UPS) batteries etc.
Dual purpose batteries are usually Valve Regulated Lead Acid (VRLA) Sealed Lead Acid (SLA) batteries - either gel cell batteries or Absorbed Glass Mat (AGM) batteries. They don't require to be positioned vertically like flooded lead acid batteries, they are almost maintenance free, and very tolerant to vibrations and shocks - they will tolerate electric and physical abuse, just don't push them to hard (don't hit them with the hammer, anchor, chain, rock etc.).
Dual purpose marine batteries don't have to be lead acid batteries. With the improvement of technology, lithium batteries are present more and more on boats, yachts and ships, not only for powering small electronic devices, but also as main boat battery/battery pack.
Lithium batteries have many advantages:
- they are 70-80% lighter for the same amount of stored energy,
- they have 5-10x longer lifespan regarding number of charging/discharging cycles (discharge up to 80% of declared capacity),
- they come in common group sizes or have foam, rubber or plastic spacers,
- they are designed and built as direct VRLA SLA battery replacement - just replace 'old' lead acid battery with the new lithium battery.
- zero maintenance.
To help people transition from lead acid to lithium batteries, most lithium marine batteries come with onboard electronics featuring:
- discharging over-current protection,
- charging over-current protection,
- thermal protection,
- overcharge protection,
- over-discharge protection,
- standard heavy-duty terminals.
Such electronics enables connecting lithium batteries in parallel (which SHOULD NOT be done with lithium batteries without electronic protection) for obtaining higher capacities or in series for obtaining higher voltages. However, before even considering doing something like that, be sure to read thoroughly the manuals or consider contacting the manufacturer directly - batteries come with various electronic circuits and there are many similar models of 'almost' the same batteries. We emphasize 'almost', because just one different letter in the name of the battery is perhaps all that stands between 'job well done' and the 'fireworks' on your boat.
If unsure, hire a professional to do the job for you.
Long story short - if you need new dual purpose battery for your boat, go for tested and reliable sealed lead acid batteries. Such batteries are heavier, but are cheaper and weight difference means little on the boat. In fact, such batteries are positioned low in the boat and increase the stability of the boat.
If you need light and powerful battery and don't mind spending few extra dollars/euros, go for good lithium iron phosphate (LiFePO4) or similar lithium marine battery - such batteries can be used on small boats, kayaks, golf carts, RV and ATV and similar vehicles, where extra few pounds/kilograms means a lot.