E MTB Charging in the wild

To explain a little the above answers:

Watts is a unit of instantiations power. To get power in watts, you simply multiply voltage (in V) by Current (in A). Your charger outputs 42V, and gives a range of current, but seen as the voltage in NZ (230V) is near the upper end of the voltage range (240V), lets used the upper limit. 42 times 4.6 = 193.2W. If we assume the charger is 95% efficient, you will need 203W of input power.

A 150W inverter like the one you have linked to, will simple not be able to supply this load, and will turn itself off to protect itself from damage. As such, you would need to source a slower charger or a bigger inverter to get this done.

Also not that inverter is modified sine wave, which should be OK for a switch mode power supply, but sometimes can cause weird issues.

Watt hours (Wh) is a unit of stored energy. Can be calculated by multiplying Power (in W) by time (in h). So 2 hours charging at say 180W (allow a little for energy loss from heat etc), would add 360Wh of energy to your battery pack, just over half it's capacity.

The first response above, points out that a typical 18v power tool battery doesn't have that much energy in the scheme of an Ebike battery. If the inverter was grunty enough to use that charger, a 4Ah, 18v battery, would go flat in about 20 mins, only long enough to lift your state of charge on your e-bike battery by 10 percentage points.

If you really want to do this with Ryobi gear, they have a Great inverter for their 36V battery packs. It's rated at 300W, and it's pure sine, so much better than their 150W modified sine 18V battery topper. As 300W is bigger than 205W, it should run your e-bike charger without issue.

https://www.bunnings.co.nz/ryobi-36v-300w-battery-topper-inverter_p0254211

Pair that with the 12Ah, 36V battery (420Wh), and you have enough power to add roughly 50 percentage points to the state of charge of your ebike battery.

https://www.bunnings.co.nz/ryobi-36v-hp-12-0ah-battery_p0404989

Note that this gear is expensive (Inverter $199 + battery $569 + charger ($199 new, $60 - $80 used)

And kinda heavy. Bunnings lists the shipping weight of the inverter as 0.84kg, and the battery as 2.6kg (item weights will be a touch less with packaging removed.)

Also doing this charging trailside is going to be quite time-consuming. Roughly two hours to charge the battery by 50 percentage points. (Would be interesting to see if E-bikes can take charge while you are riding, If so, this wouldn't need to be down time)

Some alternatives:

Just live with the capacity of your current battery (either by dialing back assist, or riding shorter distance in the session). Obviously the cheapest, most lightweight option.
Get a second matching battery. An expensive option (and not possible to pull double duty with your power tool needs), but you double your range in a 10 second swap, rather than spending 2 hours charging to get a 50% boost. And more weight efficient as you are not lugging the charger & inverter around. I think the below is the same battery. $1,600 & 3.7kg
https://ebiketeam.co.nz/shop/spares-parts/shimanobatterybt-e8036630wh/
Get a second smaller battery (assuming it fits): $1349 & 2.9kg
https://ebiketeam.co.nz/shop/spares-parts/shimanobatterybt-e8035forsteps504wh/
Use your car as a power source (If you are driving to say a mountain bike park, and can come back to your car for lunch. Obviously no good if you are doing long distance bike touring). Either use your current charger the cars inbuilt AC power output (on something like a BYD atto3, or Kia EV6), Using a 12v inverter. (below link is for the Adventure kings pure sine inverter 500W. $150, with free delivery). Note anything over about 120Watts is to big for a cigarette lighter, so will need to have wires run, or be run off battery clips.
https://www.trademe.co.nz/a/motors/caravans-motorhomes/parts-accessories/batteries-inverters/listing/4070387033
If a petrol/diesel car it will need to be idled (or battery voltage monitored) to avoid flattening the start battery).
Could also source a 12v ebike charger, but they seem to be rarer and slower than AC chargers.
If you were clever you could rig up some way to charge your ebikes while driving (charge wire out the tailgate etc?), Meaning you could ride the morning at one place, and the afternoon somewhere else, with say an hour of charging time as you travel between.

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Scott3

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