How Hitachi’s New MultiVolt 18V/36V Batteries Work

I visited Hitachi Power Tool’s headquarters in Braselton, Georgia last week. Hitachi invited ToolGuyd and several other tool reviewers to learn more about Hitachi Power Tool’s future, and to try out some of their new tools.
Transparency Note: Hitachi covered my airfare, hotel accommodations, and food.
While I’m still sorting out many of the details, one thing that I’m prepared to talk about is the MultiVolt battery platform they will be introducing to the US this year. Stuart talked about Hitachi’s MultiVolt platform back in October, and it is already available in other parts of the world, but the new batteries and many of the tools will be different from what is available abroad today.
Before we get into the operation of the battery, here’s a teaser list of the 36V tools Hitachi says they will release:
36V MV Triple Hammer
36V MV Hammer Drill
36V MV 7-1/4″ Circular Saw
36V MV 1/2″ and 3/4″ Impact Wrenches
36V MV 4-1/2″ Angle Grinder
36V MV 1-9/16″ SDS Max Rotary Hammer
36V MV 10″ Sliding miter Saw
36V MV Reciprocating Saw
36V MV 10″ Table Saw
MultiVolt Operation
The MultiVolt batteries will be based on 4.0Ah 21700 lithium-ion cells, and not the 2.5Ah 18650s they are currently using for their MultiVolt batteries abroad. This means that they will have a capacity of 8.0Ah when configured for 18V operation, and 4.0Ah when configured for 36V.
Why 21700 Li-ion battery cells? For that 1 mm bump up in diameter, you get 10% more volume than a 20700 cell. And compared to a 18650 cell, a 21700 cell has 47% more volume. While capacity goes up proportionally with area, the ability of the cell to dissipate heat also increases as the cell gets larger. The better the cell can dissipate heat, the more current you can pull out of the cell.

Above, you can see the Samsung 18650 cells inside one of Hitachi’s current 3Ah batteries. We weren’t allowed to take apart any of the new MultiVolt batteries, and they wouldn’t say who the manufacturer was.
What I’m really excited to talk about is how they switch from 18V to 36V. I find the method less clunky than the Dewalt FlexVolt system, and actually quite elegant.
To remind you, Dewalt FlexVolt batteries use an internal switch that is actuated by the connector on compatible tools or the shipping dongle. Depending on what a FlexVolt battery pack is connected to, its 2 banks of 5 cells are connected in series, parallel, or are totally disconnected, to get around Watt hour limitations for shipping.

With the Hitachi MultiVolt batteries, the two banks of 5 cells aren’t connected inside the battery at all. There are split connectors that bring out each bank of 5 cells to the tool. If you connect an 18V tool to the battery, it simply bridges the split connector and connects the two banks of cells in parallel. If you connect a 36V tool to the battery, the tool has a matching split connector that allows the tool to wire the two banks of 5 cells in series, giving the tool 36V.

I am not certain about the internal wiring configuration of the batteries, but above is one possibility of how the tool might connect the two banks of cells together in series to create 36V.
I would have to assume that if Dewalt can come under 100Wh shipping guidelines by internally disconnecting the banks of cells and calling them separate batteries, the new Hitachi MultiVolt batteries would be also immune because the banks are never internally connected.

The batteries will work with any current Hitachi charger that can charge 18V batteries. The charger simply bridges the contacts and connects the two banks of cells in parallel, making it look like an 18V battery.
The MultiVolt batteries also have the same venting the 18V batteries do, so the charger can draw air through the battery while it’s charging to cool the cells.

You can see how an 18V battery won’t fit on a MultiVolt tool. The batteries use the same rails, but there’s a tab on the MV tool connector that won’t align with the 18V battery. I also like this approach. That way all battery slots on the tools can use the same design, if they wanted to upgrade the electronics in a tool to 36V they could just change the connector without having to retool the mold.
Other Features
From Left to Right: 18V 3.0Ah, 18V 6.0Ah, Multivolt BatteriesThey did not tell us the specific weight of the new MultiVolt battery weight, but they gave us this analogy: the difference in weight between the MultiVolt battery and the 18V 6.0Ah battery is about the same as the difference between the 18V 6.0Ah and the compact 18V 3.0Ah battery.
Left: 6.0Ah battery. Right: MultiVolt batteryIn the above photo you can see the difference in footprint between the 18V and MultiVolt battiers. *note the MultiVolt battery has the incorrect label, the model number will be 36B18 not 36A18 and it will be rated for 4Ah at 36V.

MultiVolt batteries will ship with a built-in battery meter! This is actually a photo of the 2.5Ah MultiVolt battery based on 18650 cells. This isn’t the battery that will be sold in the US. It’s the best photo of the battery meter I had, though.
Unfortunately we were told that 18V batteries won’t be getting a battery meter anytime soon. They are trying to keep the price down so they can sell them at the $30 and $40 price points.

How much is this new battery going to cost? Hitachi has tried to shake up the market by dropping the price of their compact 3.0Ah battery to $40. They talked about that move while we were there. They don’t want battery cost to be an impediment to people trying their tools.
With that in mind, they set the every day retail price of the MultiVolt batteries to $99. You’ll also be able to buy a starter kit with 2 MultiVolt batteries and a UC18YSL3 rapid charger with USB port. You can buy the same charger now for $60, and so presumably the starter kit would be $260 or less.
The MultiVolt platform is due out in September 2018.
What? AC Adapter!?!
I separated this last part out because they did not give us any evidence such an adapter existed. Yes they claimed there would be an AC adapter that you could plug into the 36V tools. They did not give us any more information except say it would be launched with the rest of the platform in September.
First Thoughts
Hitachi didn’t say anything about how they are monitoring the cells in the battery pack, and so I’m just speculating at this point.
One thing that really intrigues me about this new battery voltage switching configuration, is the possibility that they could monitor every cell in the battery. With a 5 cell battery, say their 3.0Ah battery, where all the cells are connected in series, it is trivial for the battery to be able to monitor the voltage in each cell. But in a 10 cell battery, say their 6.0Ah battery, where each cell is connected in parallel to a companion cell, the battery pack can only monitor the combined voltage of the pair (or triplet in the case of a 15 cell battery).
One company I talked to claimed they monitor all the cells in a 10 cell pack, but I never heard back from them when I pointed out that wasn’t possible in their pack.
Does being able to monitor all the cells in a 10 cell pack buy you anything as a consumer? It could give companies better failure data on returned batteries and allow them to improve their battery technology. Or the battery could warn you sooner that it is having a problem with one of the cells so it doesn’t fail on you in the field.
The elephant in the room is the AC adapter for the 36V tools. As hey did not have hardware to show us, I remain very skeptical. I will say that with a 36V platform, it might be more possible than with an 18V platform, but I have my doubts it will be small enough to be practical on a tool like a drill.
Some quick back of the envelope calculations: it’s not unheard of to pull 50 Amps in a 18V tool, so the secondary windings of the transformer will have to be 10 gauge to carry 25A. That’s not a small transformer. To save size and weight at the tool, you can’t just throw the transformer at the plug like some AC adapters do, because you’d still need a somewhat unwieldy 10 gauge cord between the tool and the wall.
So we’ll wait and see what tricks Hitachi has up their sleeve with the AC adapter.

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