FT-817 Internal battery ideas

These days, FT-817ND units are supplied with the Yaesu FNB-85 battery pack. This pack consists of eight NiMH AA cells in a shrink wrapped package. The rated capacity of the pack is 1400mAh. NiMH cells have a nominal voltage of 1.2V, so 8 times this is 9.6V.

The capacity of this pack gives me about an 1 1/2 to 1 3/4 hours during a SOTA activation. SOTA activations at the moment can involve a lot of CQing, so my rough estimation is that I would be looking at a TX duty time of at least 30%. I also have a BHI filter installed, so my 817 is heavier on current draw on receive – about 417mA with the volume down, and 430mA typical on receive. Obviously more on TX. This leads me to believe that at the moment, I am getting capacity “in the ball pack” of the rated capacity.

Quite a number of my trips involve multiple activations on a single day or trip, and the internal battery is not enough to keep going the whole time. At the moment, I supplement the operating time I get from the internal battery by using either LiPo packs or three LiIon 18650 cells in series in some PVC pipe, and then plugged in via the external DC jack. This is meeting my needs for the moment.

There is no doubt that by using 3 cell Lithum technologies, there is plenty of options for external power. What about internal – when the FNB-85 dies sometime in the future, I will want to replace it, but I want something better. Given that it is working well at the moment, it would be a little indulgent of me to replace it now, so I won’t – but it is nice to have a plan. It is also nice to have more capacity than 1400mAh. Something north of 2000mAh, perhaps even 2500mAh should be achievable.

A LiPo pack in the internal battery slot

Glenn, VK3YY experimented with putting a Turnigy LiPo inside the FT-817. See his picture below:

Turnigy LiPo 2500mAh battery

This battery can be found at HobbyKing at:


It has a lower C rating than many LiPos as it is optimised for RC transmitters, rather than the boat, plane, helicopter at the other end that could be drawing 100A plus. The FT817 is going to only hit it with 2A, which is only 0.8C – a walk in the park given its 5C discharge rating. The voltage of the pack would be 12.6V fully charged and 11V or so when discharged – so the voltages will be perfectly fine for the 817. Some care is needed as the battery will provide some additional operating time down to 9V, but this is not recommended. The operator needs to pay attention to the voltage display on the 817 screen. The 817 cutoff is 7.5V which would drive the LiPo pack too low – this is 2.5V per cell if it was perfectly balanced. If even a little unbalanced, one cell would be even lower, which is not good.

The LiPo is is a good solution, but it is a higher maintenance solution given the cut-off issue above. The FT-817 is also not designed to charge LiPo packs, so the LiPo needs to be taken out to be charged. It really needs a proper LiPo balance charger to keep the cells in line with each other. Care would need needed if this battery was installed fully charged and an external DC power supply be attached, as unless the green battery cable is connected to a meaningful voltage, the FT-817 will trickle charge 10mA into the battery. This is bad for a fully charged LiPo pack!

NiMH solution

The 817 is supplied these days with the FBA-28 battery holder. This is designed for use with Alkaline cells. These cells are not going to handle a 2A current draw very well, so I can’t imagine that there are many in the world who are using this holder in this way. The holder is pictured below:

FBA-28 battery holder

I have put in a number of Energizer 2450mAh NiMH battery cells into the holder. Eight are needed to complete the pack. The pack is a little difficult to get into the 817, but the trick is to put the holder in first empty, and then put the batteries in.

Yaesu do not recommend using rechargables in this pack. The main reason for this is suspected to be the risk of a short. The Cathode of a rechargable AA NiMH is the outer shell. Aside from the last cell in the pack, this will have a voltage difference to the case, and some of the cells can rest against the case. The only protection against disaster is the outer label on the cells, and this can be scuffed away. The picture shows that there is a plastic tab that will cover about 2/3rds of the lower 4 cells, but some electrical tape put over the exposed cells will also aid in providing the necessary protection. I would not think it needs to be comprehensive coverage, but two strips over the top 4 cells, top and bottom, and one strip over the 4 bottom cells at the exposed tops should be enough. (Of course half the cells are facing the other way so their top will be the other cell’s bottom, etc).

One final modification is the green cable. This is connected between cell 4 and 5 in the pack. If this cable remains connected, the FT-817 will not charge the pack. This cable needs to be cut and secured, and then everything will be ready to go.

Appropriate NiMH cells

My picture above shows Energizer NiMH cells. These are rebranded Sanyos. They work well in many applications, but unfortunately, not this one. Even though fully charged, the voltage drop when the 817 hits them with near 2A is too much, and so the effective life of the pack is much lower than the 1400mAh Yeasu pack. The labeled 2450mAh capacity sounds real nice, but the real world experience would suggest much different. I have tried them in non-radio applications with current draws of around 500mA, and they work ok there.

I found that HobbyKing sell NiMH cells, including some low discharge 2400mAh cells. This is a great capacity for a low discharge cell. I have also read that some have tested these cells at 3A and they work well. I am getting some of these cells to give them a test, but if they can handle 3A, they would be a great cell to use in the Yeasu battery holder. The 2400mAh capacity nearly matches the 2500mAh LiPo pack. Both solutions should give nearly 3 hours of heavy SOTA activation time, but the NiMH solution can use the internal Yaesu charger (2x 6 hour charges back to back), and there are no concerns about damaging the pack if taken to 8V or so.

Wayne VK3WAM


17 comments on “FT-817 Internal battery ideas

  1. waynemerry says:

    I have used the HobbyKing NiMH, not in the FT-817, but in other high current draw applications. It significantly outperforms any other NiMH battery I have used, both in actual capacity to labeled capacity ratio (it’s very good), and in ability to supply high current. I think these cells should perform well in a FT-817. They cost less than $1.50 each, so it’s not exactly a high risk option to get eight of them.

  2. […] A while ago I wrote about options for internal batteries in the FT-817. As detailed in that post, some are trying out LiPO options in the FT-817, and HobbyKing sell a 2600mAh 3S option. Provided operators watch the voltage level on the FT-817 screen to avoid excessive discharge, that would work well. […]

  3. Beric Dunn says:

    Thank You! I’ll have to get some on order.

    Thank you for doing the hard work for us 😉

  4. boletomail says:

    Very good tips, thank you from Brazil. 73s

  5. Jon Biddell says:

    Hi Wayne,

    I’m just about to buy an FT-817ND from Ross at Strictly Ham, so this battery information is particularly useful to me.

    I have an idea for a larger battery pack – one which would be external, but connected through the battery holder rather than the DC jack – imagine a “slab” of Lipo batteries the size and shape of the 817, with a “lump” on top that slips into the battery bay of the 817 and site under the radio. Yes, you’d have to externally charge it, but do you think this is a viable idea ?


    • waynemerry says:

      I wonder what you gain by having it connect through the battery holder when it is external. The 817 is quite happy being fed from a 3S LIPO through the external port 12.6V fully charged down to about 11.0V when at the LIPO “hump”. I’ve used the FT-817 with no internal battery at all installed to save some weight – works fine – only need to ensure that the connector is well inserted because the radio switches off immediately if the connection is loose!

      • Jon Biddell says:

        Probably none at all actually, I was thinking of it more from an aesthetic point of view. Also when packing it into a backpack you wouldn’t have anything like external wires, etc to snag on anything. It was just an idea.

  6. streamertyer says:

    I would try the LiPO battery shown and cut the positive lead to the radio and install 5 series 3A diodes in series to drop the voltage to the 817. That should be enough to have the radio shut off once the battery hits 11v.

    • waynemerry says:

      It’s a lot of heat to generate across the diodes and for this heat to then have to be dissipated. Say if you have 0.7V across each diode – so 3.5V. You are looking at about 30% or so of all of the energy stored in the battery being burnt on the diodes. If you have a 2600mA 3S LIPO, you are looking at about 10kW/h to burn – that’s a fair amount of heat!!

  7. What do you mean by (2x 6 hour charges back to back) in the last paragraph?

    • waynemerry says:

      The FT-817 charging function is purely time based. A 2x 6 hr back to back charge is a 12 hour charge. The charging rate of 2400-2500mA AA NiMH with the internal charge function is slow enough that it would take 12 hours to charge the cells from flat. You would want to ensure that the cells are flat before starting. If you overcharge, the cells get hot as the excess energy is converted to heat. So if you were wanting to try this, check on it to ensure the cells are staying cool to warm and not hot.

  8. gordonhudsonnu says:

    Any experience with low self discharge alkaline rechargeables? I use these in wildlife cameras (camera traps). The ones I use are rated at 2500ma/hr and are made by Vapex, although I see they do higher rated ones now. The advantage is that they don’t lose charge when sitting idle, and they are charged when you buy them (although in my tests maybe to only 75%). They are supposed to be OK at higher current loads, but I have never tested that. I don’t know if they might need separate charging arrangements.

    • waynemerry says:

      No experience with these – however the chief problem I have had with alkalines in general is they start heading for the short cycle exit as soon as current draw is > 250mA. NiMH are better, depending on the brand.
      I’ve been using NiZn from HobbyKing in the KX1, and 8 of these could be used in a FY-817. The extra voltage is being wasted :(, but they seem happy at higher current draws

      • gordonhudsonnu says:

        Actually I meant “low self discharge rate” NiMH cells. I have loads of the Vapex 2500ma/hr ones for use in wildlife cameras. They seem to work well in low temperatures and can handle quite high current spikes, but they are only 1.2v. 8*1.2V=9.6V which is at the bottom end of acceptability for the FT-817. However, I have seen charts that show the radio is more efficient at lower voltages. The ability to fit in an extra cell or two in would have been helpful. I think the reason they did the eight cell pack is that historically they did this with the original FT290R, but it was C type cells. The radio charged those internally in the tray.

        • waynemerry says:

          If they are happy on the higher current spikes, then give them a go. 9.6V is plenty for the FT-817. Most of the radio is driven off a 8V bus anyway – linear regulated – so running on 8 of those cells – provided that they can handle the up to 2A draw, will result in a cooler radio with little excess voltage being burnt at the regulator.

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