The solar panel upgrades seems pretty useless, what with only decrease the charge time on top, which is already pretty fast. Maybe replace them with an upgrade that increase the amount of battery power from the pickups that well giver bettery power underwater? That would both allow it to increase a bit (but not as reliably as the max battery capacity), how far you can dive, while still reducing the charge time to some extend at the surface (since you also pick up battery charge pickups on the way up, so you gonna end up with more battery when you arrive)