I have the BlueROV2 with the original charger and battery plus just bought the newer charger and 2 new batteries. I’m told by our hazards shipping staff that the batteries need to be at 30% charge to send by DHL/FedEx overseas. Is there a way with the charging system to draw them down without putting them in the ROV and running it in a water tank?
Hi @bobbowen, welcome to the forum 
Our H6 Pro Charger supports both internal and external discharging, but that functionality requires using the “unlocked” full firmware - it’s hidden from the basic/simplified interface that the charger ships with.
Our original (black) battery has a capacity of 266 Wh, so discharging that from fully charged to completely empty using the charger’s internal maximum of 30W would take a bit less than 9 hours. 70% of that would be a bit over 6 hours, and less if your batteries are already partially depleted. The new (white) batteries have a lower capacity of 230W, so would be a bit faster.
External discharging can be much faster, but requires attaching a high-power load that can use up energy quickly.
Hi,
Do you have directions for using the old charger to discharge the original black battery? I’ve got it in the ROV now with just the lights on but that is not discharging much.
The old charger usage manual also includes a section on discharging
Note that both the old and new chargers should work for both the old and new batteries, but care must be taken to ensure the correct voltages are selected for the chemistry of the connected battery. Our old black and new white batteries are both Lithium-ion, and our new rectangular black battery (which I don’t believe you have) is Lithium Polymer. I’d recommend double-checking the safety section on the relevant product page before doing any charging or discharging.