Lead-carbon batteries explained

A lead-carbon battery is a lead-acid battery whose negative plate is enhanced with high surface area carbon. That carbon gives it supercapacitor like behaviour which highly resists sulphation (the main cause of wear on a lead-acid battery), so it survives sustained partial state of charge (PSoC) operation and delivers several times the cycles of a standard AGM, while keeping lead-acid's price class, safety and charging profile and recyclability.

Why the carbon matters: the failure mode for AGM in a use such as daily solar is sulphation at partial charge. A solar charged bank in a New Zealand winter can go weeks without reaching a complete full charge, cloudy day after cloudy day, each one ending at 60 or 70 percent full, and on a standard negative plate lead sulphate crystallises and hardens exactly under those conditions. The carbon on a lead-carbon negative plate provides an enormous surface area that keeps sulphate deposits small, soft and recoverable, and it buffers the charge rate that lets the battery absorb energy rapidly when the sun does appear.

The practical result is a chemistry built for exactly the duty cycle that off-grid New Zealand actually runs. The numbers are on the product pages: the C2 CARBON is rated 4500 cycles at 30 percent depth and about 3000 at 50, and the PROFLEX 6000 cycles at 30 percent, 4000 at 50 and 1500 at 80, against about 1500 and 620 cycles for a standard NOMAD E2. Fast charge acceptance comes with it, and it isn't a small difference: the 220Ah C2 CARBON takes up to 65A and the 200Ah PROFLEX up to 120A, where a 270Ah E2 tops out at 50A. So when the sun does turn up after a cloudy week, a lead-carbon bank can actually use all of it. There are no battery management electronics required, the charge window is the same 0 to 40C as our AGM, and end of life goes through the same near total lead recycling as every other lead battery in the country. Weight is still there though, because lead-carbon weighs what lead weighs, which is why it is the pick for stationary banks.

One thing worth being clear about: lead-carbon uses AGM construction, the same sealed lead-acid construction with a carbon enhanced negative plate. The performance difference is large enough that it is treated as its own battery type. Where we specify it: home and shed storage for off-grid houses, telecom and pump sites that cycle daily on solar, and any bank that spends winter at partial charge. We stock it as the NOMAD C2 CARBON in 85Ah, 140Ah and 220Ah, and the PROFLEX 200Ah, which carries a seven-year warranty rather than the five on the rest of the range. Where we don't specify it: installs with an extreme lightweight requirement, which is where lithium would be best. Between AGM and lead-carbon for a solar bank the question is simply how often you use the site and how often the bank will reach a full charge. The more you use it, choose lead-carbon, sites that don't reach full charge all the time use lead-carbon, else AGM is fine.