You may be able to ask your controller to give less power, that will take the strain off the battery. You'll obviously lose the maximum power that way, but might avoid the cutouts. Could be a cheap short term solution good for a year or more while you think ahead.
A more efficient hub may be more cost effective in the long run. The 1000w hubs tend to be very cheap to buy, but the advertisers naturally don't stress the downsides: illegal for almost all uses, the need for a large good quality (expensive) battery that may need replacing fairly often, and that even with all that power it won't be very good at hill climbing.