Dyson DC16 battery replacement

[aurmer]

I have had this DC16 for years. When I bought it, the battery life was disappointing. I understand that with this kind of power, no battery will last all that long. You can get more context reading product reviews on amazon.

http://www.amazon.com/Dyson-DC16-Handheld-Vacuum-Cleaner/product-reviews/B000I5Q1IC

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That said, I am wanting to convert this device to wall power by purchasing (or building?) a power supply for it. My problem is figuring how much power I need. Here is what I know.

The battery is rated at 21.6V.
The battery measures around 24V when charged.
The battery measures around 12-15V while the vacuum is running.
When I hook up my lab power supply at 24V to run the vacuum, it rails out at 5A and the voltage drops to about 12V. While powered this way, the vacuum motor sounds like it is running at half power compared to the noise produced when running off the battery.

Is there any way for me to anticipate my power needs? Other than buying an expensive 'high-power' variable power supply for testing?

https://www.amazon.com/dp/B00KTJE3L4/ref=wl_it_dp_o_pC_nS_ttl?_encoding=UTF8&colid=13WJQDDHQBIXA&coliid=I1PIV4Z1HJ88PT
By the way, I have tentatively selected this power supply. Can anyone tell me why this might be a bad choice? I understand that the motor is an inductive load, but I am using Dyson's original motor driver circuit which I assume handles any issues (I hope?). Experienced advice is appreciated before I waste money/blow something up. =P

[NiHaoMike]

Look into converting some surplus server PSUs. Cheaper and higher quality.
http://www.tjinguytech.com/my-projects/diy-24v-47a

You can also use 6 R/C lipo cells and reuse the existing protection board.

[Buriedcode]

At 21.6V thats 6 3.6V cells - often "lipo's" are 3.7.  The motor won't care but any charging or protection circuit should be rated for the cells you use.

As for the motor, I'm not sure if these use BLDC because their silly marketing spouts all sorts of crap about 'v6 digital motor', but I'm assuming it is.  I guess if the current battery is working, then just measuring the current draw to get an idea of power requirements - I suspect its pretty hard on the batteries because then they can charge a lot for replacement battery packs.