Backup smaller supplemental battery for extended range

[McQ]

I am currently using a 48 V 17.5 AH 840 WH Jumbo Shark battery from BafangUS Direct . Even with some very conservative riding (pedaling on flats and always coasting on downhills) I find I need just a bit more battery to get back to my vehicle or home. Peddling of course is an option , but with the weight of this bike (sometimes I pull a trailer behind with camping gear) and its gearing ( no little chainring) I would not be able to pedal up some hills at the end of the ride. Ebike itself is a converted Salsa Mukluk Ti with Bafang BBSHD motor. Is there a small backup battery available which I can easily plug in to finish rides?
thanks
Chris

[73Eldo]

How many miles are you getting? Then how much more do you need?

[McQ]

Not sure, it really varies with the topography of any given ride . Lets say I can ride for 3 hours and need 3.5 hrs .

[Retrorockit]

I had a BBSHD with a battery like that. I know what you mean. Great on the way out and sweating bullets on the way back. Over time it will only get worse. BBSHD needs a big battery, otherwise you can't make much use of the extra power. I ended up going to a 24AH 21700 battery 1150Wh. Life is good. The battery wears me out instead of the other way around. Maybe you can find a 12Ah that fits the same bracket. I would ask the vendor you got that one from. Should be plug and play.
Be sure before you buy. I have 4 bateries and 4 different brackets.

[AZguy]

I have mounts for two batteries, one on the downtube and the other on a rear rack... works great for extended range although frankly it's only very, very seldom necessary but definitely alleviates any range anxiety concerns since the range with two is more than my sorry body could ever do... switching between them is as easy as moving the motor input from one connector to the other and the connectors are conveniently located under the seat

[CarbonFolderBBS02]

I run a back-up battery , a Samsung cell battery 6AH pack under the seat in a saddle bag. I have a Luna Shark pack on the frame 13.5AH (LMG Cells).
https://lunacycle.com/luna-mighty-mini-battery-bag/

The luna battery bag fits perfect and tight to the seat and post.

I got the battery pack from jonnynerdout , I think he's sold out , like everyone else. There is another on EBAY (USA builder) that makes Samsung 8AH saddle bag batteries.

https://bicyclemotorworks.com/produc...ocket-52v-6ah/

[73Eldo]

Not sure, it really varies with the topography of any given ride . Lets say I can ride for 3 hours and need 3.5 hrs .

17.5ah pack I would estimate would get you in the 35 mile rage so that fits with 3 hours but I could see that the extra 1/2 hour just isn't there most days. A 21ah could maybe get you there. Planning another build? That's what I did. I use my original 12ah pack for the 'off road' bike that gets ridden hard but not usually that many total miles. The 17-21 is on my street bike and my ass wears out long before the pack does.

Do you have any cordless tools or equipment? I have read about some people that have adapted power tool and garden equipment packs to work on a bike, capacity is normally limited but if you are just looking for a boost and already own the other batteries may be worth considering. I have thought about going the other way, mod the garden equipment to use the bike packs. I have seen some older garden equipment for sale cheap because they don't have good batteries or chargers. Maybe that's another excuse to buy another big bike battery?

[McQ]

Thanks for all the suggestions
In considering weight , price and trying to keep with the same mount and voltage (48v) looks like I have 2 options and perhaps a 3rd? :

1. Purchase smallest 48 V I can find which so far is Bafang USA's Ultra Slim Shark at 11.6 ah as supplement which I would have to carry at 7 lbs $450.00 + 10 lbs ( current 48V 17.5 ah) total 17 lbs.. ouch!

2. Purchase Whale Shark 24.5 ah Whale Shark 12.5 lbs @ $1200 ouch ! and try to sell my 17.5 Jumbo Shark ? Do people even buy these used?

or perhaps use a tool battery somehow ? I have many 5.0 ah Makita batteries. Here's the info I found below . I can't quite decipher how to connect the makita adapter to my BBSHD
https://www.electricbike.com/cordles...ies-for-ebike/

[AZguy]

There are smaller batteries although with supply chain issues maybe hard to find and frankly an 11.6Ah is a nice size - for me large enough for most rides although I pedal all the time and seldom cruise much faster than 15-16mph

Used batteries are a tough sell and would really doubt you'd see a good return doing that. It's very difficult to trust a used battery and they are hard (and expensive) to ship (at least legally). If you kept logs it would help resell but I still doubt you'll get a good return even with logs.

I wouldn't even consider tool batteries but that's just me. There are many very good reasons there are bike specific batteries and I'd stick with them.

[Retrorockit]

The 24Ah battery Is going to have a weight penalty also.It will probably cost the same as both other batteries together. My 24 Ah 21700 battery weighs 14# in 18650 it would probably weigh more.. It was about $650 but is NLA from that source ( I may have bought the last one), and the bracket sucks. The weight is always there with the big battery. With 2 compatible batteries you have the option of running light or heavy as desired. A BBSHD with a trailer in the hills is going to need a big battery. It is liberating for me to take a 30 mile ride into 25mph headwinds at 25mph speed and not worry about range at all. It will probably be even more rewarding for you.17.5Ah+11.6Ah= 29.1Ah.................Redundancy is an advantage in itself. Especially far form home.
Buying the big battery 1- Is always heavy,2- is costly both for purchase, and resale of you existing battery.
The DIY scheme is problematic because you need to end up with a battery that can produce 30Amps continuous power for the BBSHD. Fire is a possibility. I would leave that to the 350W Ebike riders.

[McQ]

I think I found what I need in a back up battery with a 52V 50AMP 8AH 21700 MINI-MAX E-BIKE BATTERY from electrify bike .com

Onto the next issue which I think is my display. I have a Bafang DPC-07 which came with my BBSHD kit. I like everything about it except one very important thing ..... the range indicator is off by quite a bit. My battery when put on charger reads 52.9 so 90% , but display at 50%.?? Is this as simple as replacing with display that will show voltage? If so , any recommendations?

[AZguy]

The battery "level" indicator is just a voltmeter bargraph. The display is likely set for 52V battery which would be why the 48V battery always reads low. This may or may not be able to be changed in the display settings.

Putting a digital voltmeter on the bike (pretty easy) or if the display supports a digital display vs. bar graph (some do) you are almost always much better off

In case you aren't aware you do need to charge your batteries to 100% every few cycles to keep them balanced