Solar is the purest deep-cycle application in the industry: the battery is not waiting for an emergency, it is working a daily shift — charged by the array through the day, discharged through the night, at a depth set by how honestly the system was sized. XD Battery’s solar deep cycle offer is drawn from two documented lines that share the cycling discipline: the lead acid deep-cycling series (12V blocks at 100Ah, 200Ah and 250Ah tiers) and the solar gel series (12V 100Ah, 150Ah and 200Ah models documented for solar systems), each with three-year warranty documentation on the named models.
The sizing method, once and for all
Begin with the night load in watt-hours — the energy the battery alone must deliver between sundown and useful sunrise generation. Divide by system voltage for the amp-hours to be replaced daily. Then choose the depth of discharge you will design around: the standard engineering bargain is 50%, meaning the bank’s nameplate capacity is twice the daily draw, trading battery spend against cycle life in the ratio every datasheet rewards. Multiply by autonomy days — the consecutive sunless days the system must survive, typically one to three for homes, more for critical loads. The result is the bank size; the block choice (gel for heat and unmanned sites, deep-cycle flooded-discipline sealed blocks for attended value) follows from the site, not the spreadsheet.
| Daily draw 1 kWh @ 12V, 50% DoD, 1 day autonomy | ≈170Ah → two 100Ah blocks, or one 200Ah-class block |
|---|---|
| Daily draw 2 kWh @ 24V, 50% DoD, 2 days | ≈335Ah @ 24V → two strings of 200Ah-class blocks, or a 2V cell bank |
| Daily draw 5 kWh @ 48V, 50% DoD, 2 days | ≈420Ah @ 48V → OPzV/OPzS 2V string territory, or 51.2V storage systems |
The charge side has its own discipline: the array and controller must return the daily draw plus losses on an average day, and the controller’s charge profile must match the chemistry — gel banks in particular want their lower absorption voltage respected, a setting error that silently taxes cycle life for years. Where the project is a complete system rather than a battery purchase, the battery-for-solar-system page takes the whole-system view, and the off-grid page handles the no-grid-at-all case.
Deep cycle or gel for a rooftop home system?
If the batteries live in a ventilated indoor space and the system is attended, deep-cycle blocks are the value answer. Outdoor cabinets, hot climates or unmanned sites argue for gel. Both are documented on this site; we will quote the pair.
Can I start small and add blocks next year?
Age-matching discipline says a bank is one age. A planned two-stage build should buy stage two early or accept a second, separate bank. It is cheaper to oversize the first bank than to blend ages.
What kills solar batteries fastest?
Chronic undercharge — an undersized array that never quite refills the bank. Size the array to the battery, not only to the load.
A last word on expectations: a deep-cycle bank sized by this method will still meet its hardest week in the worst month of its worst year — that is what the autonomy multiplier is for. Size honestly, charge correctly, and the bank becomes the most boring part of the system, which is the highest praise solar hardware can earn.