If they are, you could put your protective ground a couple batteries from one end. Then you'd have a -24v system and a +36v system. B-) Put the batteries in separate boxes and only bring the two "halves" together at the inverter - at a covered connector.
Limit for "low voltage" is typically 50v nominal. This is because that's about as high as you can go before you start getting a grab-and-get-stuck-to-it electrocution hazard.
I suspect it's actually 50v because Bell figured that out and standardized on 48V (to minimize copper usage within the constraint of not electrocuting their workers), then the codes were written taking the phone company's usage into account. B-)
