At a glance: Built for boats and motorhomes, the Optima BTDC-4.2 carries the rating 55Ah 12V 765A. Technology matters here: it is a spiral-cell AGM battery.
12VNominal voltage
55AhAmp-hours at C20
765ACold cranking amps
Why choose the Optima BTDC-4.2
Cruising yachts and touring motorhomes often share the same battery code: Optima BTDC-4.2. Polarity is positive on the left-hand side, which keeps the cable run unchanged in most lockers. Matching a whole bank is easier at baterias.online, where each model keeps its exact code.
With 55Ah, it suits smaller engines and machines with few accessories. 765A gives more starting power than most batteries of similar dimensions.
Technical figures at a glance
MakeOptima
ReferenceBTDC-4.2
RangeOPTIMA BLUE TOP
Suitsboats and motorhomes
Nominal voltage12V
Amp-hours at C2055Ah
Cold cranking amps765A
TechnologySpiral-cell AGM
Outer measurements254 × 175 × 200 mm
Weighs20.6 kg
Polaritypositive on the left-hand side
Terminal type1 & 21
EAN barcode4016987113547
Optima BTDC-4.2 in everyday use
Weekend sailors often find the engine battery fine and the domestic bank flat. Set the mains charger, the solar regulator and any B2B charger to the spiral-cell AGM profile. Swollen cases or a smell of acid in the locker call for immediate attention.
How spiral-cell AGM batteries work and how to look after them
Rolled plates offer a large surface in a compact space. Off-road vehicles love spiral cells for vibration resistance. Recharge after heavy accessory use.
Quick compatibility checklist
- ✓ The capacity rating, 55Ah, should suit the consumers you run. Lots of electrical equipment calls for the higher end.
- ✓ For winter starts, 765A should at least match the old battery.
- ✓ Terminal check: 1 & 21. Spade widths and post diameters vary, so match the type exactly.
Answers before you buy
Does the Optima BTDC-4.2 have left or right-hand polarity?
This battery has positive on the left-hand side. Compare with your old unit; if they differ, the cables may not reach.
Can I use my usual charger with this battery?
Most smart chargers have a mode for spiral-cell AGM. Select it before charging; an unsuitable programme can shorten battery life.
Will my existing clamps fit this battery?
With 1 & 21 terminals on this model, cables that already fit that type need no adapter.
Are there other sizes in the same series?
It comes from OPTIMA BLUE TOP. Other sizes in that series share its construction.
Batteries with the same format
If you prefer another make, these fit the same space with the same terminal side.
Optima YTS-4.2Optima YTU-4.2Optima BTSLI-4.2
See also
Finished comparing? Placing your order online takes a couple of minutes. Bookmark this page if you want the data sheet to hand while fitting.
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