GreenWattWise LabQuestions to Ask Before Accepting a Home Battery Installer Quote
Installer quotes for a home battery are hard to compare because they rarely use the same terms. Here's what to ask before you accept one — and why it matters.
Quick Answer
Ten questions decide whether you can actually compare two home-battery quotes: usable vs. nominal capacity, the sizing rationale, the consumption and solar assumptions behind it, power rating, backup scope, warranty terms, which efficiency figure is quoted, whether future loads were considered, and exactly what the price includes. Ask them in the same form of every installer, and record the answers the same way — that's what makes two quotes genuinely comparable instead of just similarly formatted.
This isn't an anti-installer article. Most quote differences come from installers making reasonable but different assumptions, not from bad faith — the questions below exist to make those assumptions visible, not to catch anyone out.
Why This Is Harder Than It Looks
There's no industry-standard quote format for home batteries. One installer's quote might state nominal capacity; another states usable capacity. One states backup scope explicitly; another leaves it implied. None of that is unusual — it's simply what happens without a shared standard for how a quote is presented. The buyer is left to reconcile the differences, and it's easy to compare numbers that look equivalent but aren't.
The Checklist
Work through these with each installer, in this order:
Battery capacity
Ask: Is the quoted capacity nominal or usable?
These can differ by 10% or more. Comparing a nominal figure from one quote against a usable figure from another makes two batteries look more different in size than they actually are.
Sizing rationale
Ask: Why was this particular kWh size recommended?
A specific answer (tied to your consumption pattern or a stated objective) is a good sign. "This is what most people get" is worth pushing back on.
Consumption assumptions
Ask: What annual or evening/night consumption did you assume for my household?
The sizing rationale is only as good as the consumption figure behind it. If nobody asked about your actual usage, the number may not be based on your household at all.
Solar assumptions
Ask: What PV generation profile did you assume — including winter?
A battery sized around a best-case summer day can look oversized or undersized the rest of the year.
Battery power
Ask: What is the continuous discharge power (kW), separately from the energy capacity (kWh)?
Capacity tells you how long a battery can run something; power tells you how much it can run at once. A quote that only states kWh hasn't told you the whole story.
Backup scope
Ask: Is backup included? Whole-home or selected circuits? Manual or automatic? Is there a power limit?
"Backup included" can mean very different things — a few circuits on a manual transfer switch, or automatic whole-home coverage up to a power limit.
Warranty
Ask: How many years or cycles? Is there a remaining-capacity guarantee, and what conditions or exclusions apply?
A longer headline warranty period with a weak remaining-capacity guarantee can be worth less than it sounds.
Efficiency
Ask: Does the quoted efficiency figure refer to the battery, the inverter, or the round-trip system efficiency?
These are three different numbers. A round-trip figure already accounts for both charge and discharge losses; a battery-only figure doesn't.
Future loads
Ask: Does the sizing account for a heat pump, EV, or other electrification you're planning?
A size that fits your household today may not fit it in two years — see the dedicated guides on sizing with a heat pump or an EV below.
Price structure
Ask: What exactly is included in the quoted price — equipment, installation, permitting, monitoring?
Two similar-looking prices can include very different scopes of work.
A Comparison Table You Can Reuse
Illustrative example only — these are not real quotes, and the values are placeholders to show the format:
| Item | Quote A | Quote B | Quote C |
|---|---|---|---|
| Usable capacity | — | — | — |
| Battery power (kW) | — | — | — |
| Warranty | — | — | — |
| Backup scope | — | — | — |
| Estimated annual cycles | — | — | — |
| Installed price | — | — | — |
| Key assumptions stated | — | — | — |
Filling in a table like this for every quote you receive is exactly what turns a pile of differently-formatted PDFs into something you can actually compare.
Common Mistakes
- Comparing headline prices before confirming the quotes describe the same scope of work.
- Comparing a nominal capacity figure from one quote against a usable figure from another.
- Treating "backup included" as a single, comparable feature across quotes.
- Accepting a sizing rationale that isn't tied to your own consumption or goals.
- Not asking whether the sizing already accounts for planned electrification.
Before You Ask: Know Your Own Target
These questions work best once you already have a rough target size in mind — otherwise you're evaluating the installer's numbers with nothing to compare them against. The battery sizing guide (or the free size calculator) is the natural starting point before you request quotes at all.
Frequently Asked Questions
Is this guide accusing installers of being dishonest?
No. Most differences between quotes come from installers making different reasonable assumptions and describing them in their own terms — not from dishonesty. The goal here is to help you ask the questions that make those assumptions visible, so you're comparing like with like.
What if an installer can't answer one of these questions clearly?
That's useful information on its own. It doesn't necessarily mean the quote is bad, but it's worth asking again in writing, or treating that item as unverified when you compare quotes.
Do I need to be a technical expert to use this checklist?
No — the point of asking these as direct questions is that you don't need to already know the answers. You just need to know which questions matter and record the answers consistently.
This covers the questions. What if I want help applying them to my own quotes?
That's exactly what the Buyer Toolkit is for — a structured worksheet plus the Decision Calculator to check the sizing rationale against your own numbers, not just this checklist on its own.