Reddit reviews Grin Technologies Bottle Bob

To be fair to you and your legs, even the easiest gear on that bike (42t up front, 32t on the rear) is passable, but not ideal for serious hills. It's more geared for casual rides, commuting, and only mild hills.

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You have a few options for cheap kits, but keeping it under $400 without relying on potentially dodgy components isn't going to be particularly possible.

Most cheap hub motor kits aren't compatible with cassettes (your rear gearing), so you could either go with a front hub motor, or convert your bike down to a 7-speed freewheel (you'd need to buy and install a 7-speed shifter).

Whether you choose a front or rear hub motor kit, you'll need to find one that will fit in with your bike's 700c wheelset. Terms to look for when searching for a kit include "700c", "28 inch", and "29 inch". They're all different marketing names for the same wheel diameter.

Here's the cheapest one I was able to find in a very brief eBay search. It's a 500w geared motor, available for either front or rear (you'll need to convert your bike to 7-speed if you want the rear option) at $175, or $225 if you want it with an upgrade LCD display. I prefer the display, but it's not mandatory.

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Next, you'll need a battery. There are a lot of good options out there, for batteries made with name-brand cells and sold be reputable sellers. But there are also a lot of questionable sellers out there, selling packs made out of generic Chinese cells that might or might not meet their stated specifications.

The big three sellers that I would recommend are LunaCycle, EM3ev, and if you can't find a battery from either of those two (your low-step frame basically rules out a lot of the popular mid-frame-mounted battery designs), shop carefully from UnitPackPower.

Things to look for from a battery:

1. The battery's nominal voltage needs to match the designed voltage for your kit. So, if you buy a 36v kit, you need a 36v battery. If you buy a 48v kit, you need a 48v or 52v battery (they're close enough to be mostly interchangeable).
   
   
2. The battery needs to be able to supply enough current for your kit. The battery will have two current ratings - a continuous current rating, and a maximum or peak rating. If you choose not to buy from a reputable manufacturer, it's safest to ignore the peak rating entirely, because sellers like to list peak ratings that the battery might only be able to maintain for as little as fractions of a second. To avoid straining the battery, you want the battery's continuous rating to match the motor controller's peak rating.
   
   
3. For maximum safety and battery reliability/longevity, you want a battery that's made from name-brand cells. Sanyo, Panasonic, Samsung, and LG are the most common cell manufacturers you'll see when looking for ebike batteries. If the product listing for a battery doesn't list the brand of cells they're using, avoid that battery. UnitPackPower sells name-brand packs alongside generic packs, so you'll want to watch for this.
   
   To tie all of this in with the 36v 500w kit I pointed out earlier in this post, here is a battery from UnitPackPower that fits the requirements.
   
   
4. The battery is 36v nominal, to match the 36v motor kit.
   
   
5. This battery can supply 20A continuous. The kit I linked to doesn't actually list its controller's peak rating. It never hurts to ask the seller when information is missing, but for a 500w kit, 20A should be plenty.
   
   
6. This pack is listed as using Samsung cells. They're not going to be high-end cells at this price point, but at least you can be sure that they were manufactured with quality control in mind.
   
   This pack is $312 on its own, or $394 including the rear rack that it's designed to slot into. But you can always just strap it to a rack of your choice, or mount it however.
   
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   The last item you'll need is a torque arm. I'd suggest reading through this article from ebikes.ca that explains what torque arms are, and why you want one. Unfortunately, the torque arm that comes with the kit I linked to is a knockoff of an old design (the GrinTech TorqArm_V1 mentioned in the article) that was faulty in design and was discontinued in 2010. So, you'll want a better one. I recommend the TorqArm_V3. It's overkill for a 500w motor, but that's not a bad thing.
   
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   So, taking my examples from above, we've got:
   
   36v front hub motor kit: $175-$225
   
   36v13Ah battery from UnitPackPower: $312-$394
   
   Torque Arm: $30
   
   And, let's say $15 for zipties, maybe a few wiring connectors for the likely event that the battery and the controller don't come with matching connectors, that sort of thing.
   
   Total example cost: $532-$664
   
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   Caveats:
   
   In my examples, I picked the cheapest decent-looking options I found in a very quick search. You might find cheaper and/or better options that I missed, and prices and product availability are always changing.
   
   The main issue I take with my own example, is the choice of a 36v system. In the last couple years, 36v has been slowly falling out of favor, with 48v/52v systems now being more available from the reputable sellers. I picked the 36v setup because it was the cheapest I found at the moment, but if you're willing to spend just a bit more, or wait for prices to shift, you'll find a much wider range of reputable options in 48v/52v.
   
   An important topic that I didn't cover is battery capacity, and thus range. You didn't mention any particular range requirement, and mentioned hills in your neighborhood as the main obstacle, so I made the assumption that you aren't really looking for a huge battery. The 36v13Ah battery I listed as an example would be good for 18-23 miles on level ground, at 20mph, without the rider pedaling. Range will be lower with hills, higher if you pedal to help it along.
   
   Edit: If you do want to use one of the popular mid-mounted battery options, like this one from EM3ev, you could mount it to your bike's top tube using a set of Grin Technologies Bottle Bobs. I would have mentioned that option earlier, but I forgot it existed.

These mounts are pretty solid, but would require spacers to move the battery away from the curved tubes. Maybe not as pretty as some of the CNC clamps linked above though.

https://www.amazon.com/gp/product/B078T6QRQB

Here is some shameless self promotion for my wife's Sweet Curry conversion: https://www.instagram.com/p/BqAmkupAs4i/?utm\_source=ig\_web\_copy\_link

They mount onto the bottle mounts on your bike (assuming you have them). There are ways around this if you don't have bottle mounts, like bottle bobs or sks anywhere bottle mount. You can see the mount attached to the battery in the pic. Actually they make it pretty clear in one of the pics, lol: https://images-na.ssl-images-amazon.com/images/I/61GdMqKoJLL._AC_SL1000_.jpg

Edit: Oops, I should have looked at your bike pic. This is a real step-thru frame, well the kind I was thinking of.

So you have no bottle mounts it seems. You can either add your own using rivnuts, or use bottle bobs like these: https://www.amazon.com/Grin-Technologies-Bottle-Bob/dp/B078T6QRQB

I would second the comments on going with a known vender like those mentioned for the battery. I bought a kit from Amazon and a battery from Luna. Very happy. As mentioned, your current plan now going to place a lot of weight on the back. I would like at the measurements for putting the battery between the frame. It will distribute the weight much better. Grin makes some mounts that might help. https://www.amazon.com/Grin-Technologies-Bottle-Bob/dp/B078T6QRQB. For some reason I can not find them on their site but on Amazon.

On other thing to look for would be a controller that does Regen braking. While it isn't going to stop you it will add more braking power.

Good luck..

Do you think I could mount the battery on the downtube using these?

https://www.amazon.com/Grin-Technologies-Bottle-Bob/dp/B078T6QRQB/ref=sr_1_8?qid=1565989720&refinements=p_4%3AGrin+Technologies&s=sporting-goods&sr=1-8