Dyson V8 replacement batteries

last updated 2 Nov 2019
Time on high Dyson V8 Animal | Dyson.com
Spec: Max - 7 min; Extended Run - 40; Extended with motorized head - 25 Charge time 5 hrs.

Dyson V8 Absolute review: finally a cordless alternative to an upright | Technology | The Guardian
V8 will last for 40 minutes without a powered head, using the crevice tool or similar suction-only accessory. It will last up to 30 minutes with the fluffy head attached, up to 25 minutes with the traditional spinning brush head or seven minutes when in maximum suction mode.

Tests
New vac 2.8 Ah runs  8.5 min. on Max w/ motorized head
        5:10 to charge
        Old battery
 4 year old    runs 30 sec. on Max
        40 min to charge
        
Briswaye 3.5 Ah  Runs  8.5 min. on Max w/ motorized head
     3:15 to charge

Replacement batteries

2.8 Ah replacement from dyson $130

4.5 Ah Jialitt $55 4.2 (44) 1.05 lbs
 Most reviews said it was better than original
 Several failed right away.  1 didn't last any longer.
 
4.5 Ah TenHutt $56 4.1 (44)  1.06 lbs unavailable

4 Ah Powerextra new - no reviews replaced battery with 4.1 (50) $50 1.4 lbs

3.5 Ah Briswaye 4.4 (81) $50
  Reading hundreds of Amazon reviews for the many available.
   I settled on Biswaye - and 10 weeks in, I could not be happier. 
  I've only used it a couple times, but I can now vacuum every part of my house
   that I need to on HIGH. That was difficult to do with the standard battery.
 3 negative
 Melted
 OK for 1 month then only runs for 30 sec