REPLACEMENT BATTERY: They are not easy to find and expensive. Here's the good news: Eureka installed Samsung 25R 18650 lithium cells into the 21.6v battery pack. They are not the best Samsung offers, but these are solid 2500mAh batteries that Project Farm reviewed and validated. This means this battery pack should not suddenly die like the less expensive no-name Chinese vac units that use cheap Chinese lithium cells. And it you need to repack the batteries, this battery pack is doable with about $30 worth of cells (six total). If replacing, LG's MJ1 or Samsung's 35E cells are excellent performers. Just be sure to have a mini spot welder and soldering iron handy after watching some YouTube how-to videos.WALL MOUNTING TIP: If you primarily use the vac for cleaning floors, consider mounting the unit so that the brush-unit sits flat to the floor when docked. The two advantages are: 1) if wanting to switch to hand-vac use, unlatch the tube and pull the powerhead up; the tube and brush-unit assembly stay in place based on how the wall mount is designed. 2) if you want to detach the brush-unit for long-reach use, just depress the button using your foot; no hands required and the brush-unit will be ready for reconnection when you dock your vac, again hands-free. (See pic). Note: it obviously helps to have a 120v receptacle close by. I was fortunate to have power on the back side of the wall and able to add the receptacle where needed.2 Yr. UPDATE: Still working nicely. I don't use it for extensive periods (only 5 min or less). So, I'm unable to make a judgement on the battery. But the vac has been very good.2 Mo. UPDATE: I've had the vacuum now for about 2 months and I like it a lot. I stick by my Dyson V10 comparison. I've used both and this Eureka is every bit as good, if not better because of the replaceable battery. I also stick with my 4-Star rating since I believe there's room for improvement listed below. Regardless, this is a solid product that if regularly cleaned (like any vacuum) will serve you well.TIP: the battery can be a bit of a pain to pull out for someone that may not be very strong. Spraying an electrical contact oil (like Deoxit D5) on the battery's connection prongs mitigates the tight connection. In our case, we pull the battery each time to store inside (where it's room temperature and dry) since our wall mount is located in the garage where temps can swing widely.ORIG REVIEW:I have struggled with this review because I was initially underwhelmed by this Eureka Cordless Vac. However, the more I've used it, the more I like it. It may not be fair to compare to a Dyson V10 that costs nearly 2.5x that of this unit. However, they are made to do the same, so here goes:Advantages:1. Noise/Suction - at first, I was under the impression the Dyson V10 was significantly more powerful in terms of suction. Why? Because of the "Back to the Future"-like whirl when you pull the trigger. It's cool and loud and of course must be more powerful, right? Or is it? This Eureka is noticeably more quiet than the V10 but I'm not sure it sucks any less. It seems to do a decent job on both hardwood and carpet.2. Price - at nearly 2.5x less than the Dyson V10, I would say the Eureka is worth a look.3. Replaceable Battery - Given the battery reliability issues that Dyson users have reported after just a year of use, the replaceable battery on the Eureka is a plus.4. Dismount of the Brush Cleaning Head - the Eureka unit has a clever toe-tap release lever that allows for easy, quick dismounting of the Brush Cleaning Head w/o the need to bend over. This is a nice feature that the Dyson counterpart lacks.5. Wall Mount - Originally, I listed this as a disadvantage because of the lack of aintegrated power supply. However, the ease of the hook/unhook process make this wall mount one of the best features of this vac and my apologies to the engineer who designed this feature. It can only be improved with charging contacts similar to the old Blackberry charging cradles where there is no friction point to dock/undock the vacuum.6. Ships and Sells from Amazon, the new Good Housekeeping Seal of Approval.Nuetral1. Weight - is comparable to other units in this class.2. Cleaning the Catch-Jar - The process of cleaning the catch-jar is similar to others. And like ALL OTHERS, you need to keep the system clean if you want ANY vacuum to operate as expected. This is especially true on this unit since the catch-jar is fairly small, it should be cleaned regularly. To keep any vac operating at peak performance, you really need a Leaf Blower. Yes, counter intuitive, but after dumping the catch-jar contents into a trashcan, you should completely disassemble the powerhead after each use (easy to do) and use a leaf blower to clean the filters and catch-jar container. Do this on ANY vac, and you'll never complain about the unit not sucking. Note, this could be difficult for apartment/condo dwellers and subsequently, having a small catch-jar container becomes a disadvantage.Disadvantages1. Battery - Although the battery is listed as a Lithium Ion version, the unit behaves like it has a NiCad battery on-board in that once it gets to the last 1/3 of the power cycle, there is a noticeable drop in power provided to the vacuum. I don't see this with my Li-on power tools.2. The controls are not as simple as the Dyson version. On the Dyson, select the suction power and pull the trigger. On this unit, you have icons that need to be looked up in the manual as to what they mean. Carpet/hardwood w/ pics that aren't intuitive and blinking dots that represent battery level (I think). May seem trivial and may be fine for most people, unless you have a mother like I do who has a hard enough time just figuring out how to turn the unit ON.3. Fit & Finish - The pieces fit together well, just not as buttery smooth as the Dyson counterpart. The Eureka components require a little extra push to achieve a complete engagement of the components. Not a deal-breaker, but, slightly noticeable if you're coming from a Dyson cordless vac.4. Accessories - Although the accessories are OK, it would have been a plus to include an offset triangular brush as well as small motorized brush for bed mites, carpeted steps, and vehicle carpet.Improvements to Make this a 5-Star Product1. Improve the battery performance over the last 33% of the operating time.2. Keep the current wall mount design and if possible, integrate a frictionless power supply into the wall mount so that a simple docking of the vac onto the wall mount automatically charges the unit like the old style Blackberry cradles that did so with contact points. Otherwise, leave the design alone, the ease of docking/undocking makes this unit a pleasure to use.3. Pay attention to the Fit & Finish / Latching of the vac's components to operate as smoothly as the Dyson.4. Make the controls more intuitive for those that aren't tech-savvy. At a minimum, make the battery-charge-left indicator more intuitive, the blinking dots don't cut it.5. Add accessories including an offset triangular brush as well as a small motorized brush for carpeted step cleaning.Although I think a $130-$145 price tag would have been more appropriate, it's still a 4 Star product that you should consider if you're looking at this class of vacuum. If you can wait, I suspect Eureka's next version will address some of the oversights mentioned above and other top tier competitors will compete for your business as well. If these features are not important to you, you will likely be pleased with this unit and at $189, it's a clear winner over the Dyson V10.